In 1857, still stinging from both their defeat in the Mexican-American War, and their earlier loss of Central America in 1833, the Mexican government decided to take advantage of American distractions in the form of the First Asian War and the lingering aftermath of the tensions in the south.
Declaration and Start of Operations
War formally began on April 18th, 1857, when it was formally declared by the Mexican Parliament against the United Provinces. However, skirmishes had been occurring along the border since late January.
Primarily, the Mexican efforts were concentrated in the south, closer to their supply lines and centers of population, with the goal of seizing both Guatemala City, and the capital of Tegucigalpa, and then forcing a surrender. Mexican forces outnumbered the Central Americans, and were able to continually advance throughout the summer before their attack could be blunted.
Battle of Huehuetenango
Late August saw the Mexican Army arrive at the city of Huehuetenango, the first major city between the main population centers of the United Provinces and the border.
It was here, after retreating for months, that the Centrals' Army choose to make its stand. General José María Cañas, head of the armed forces in the region, knowing he and his men were outnumbered, scattered most of them into the wilderness surrounding the city, and he, along with the remainder of his troops, fortified the city, blocking off every entrance and blockading each and every house. His plan was to lure the Mexican Army into attacking his position, while his units in the wilderness harassed their supply lines. Once the Mexicans got thoroughly invested into the town, his forces outside would attack their weary forces from behind, as well as their camp. Hopefully, this would buy them time, if not drive the off outright.
The Mexican forces, under General José Mariano Salas, would, as expected, begin a drive into the town on August 28th. By the 30th, they had made great progress, controlling two thirds of Huehuetenango. It was here, after two days of fierce hand-to-hand fighting, that the forces outside launched their attack in the early morning. Achieving surprise, these forces were able, in concert with those forces holding out in the center of town, to defeat the forces in the town. However, they failed at their other objective, when a recently-arrived regiment of Mexican cavalry that had yet to be committed to the assault beat off their attack on the camp.
However, the attack accomplished its goal. General Salas was forced to pull his forces back twenty miles to the town of Colotenango, where he was forced to hold throughout the remainder of the year to get both reinforcements and more supplies.
For the Central Americans, while they had won the battle, it had been costly - most of Huehuetenango had been destroyed, and they had suffered nearly four thousand casualties, far more than they could afford. But, it did give them breathing room, and they preceded to further fortify their positions. Yet, even these positions, against a more-organized assault, would not last, and would only serve to slow them down.
Yet, other events further north would ensure that when the city did fall in June of 1858, it would be to an entirely different commander.
Battle of Flores
In the north, the Army of the United Provinces was led by General Juan Rafael Mora Porras. The Mexican Army, led by General Miguel Miramón, outnumbered them, as in the south, but here the numbers were much more equal in size.
Here, the Central Army was expected to hold its own, while most forces were directed to the south, where the main Mexican advance was. In the jungles, this was something that they could realistically achieve. However, they were not expecting to face a general with the skills of General Miramón.
General Porras set up his main command center at the frontier town of Flores, along with most of his defenses in the region - he, with good reason, wrote off the jungles near the northernmost borders as being indefensible. However, he also did the same in the region around Flores. So, while his defenses could not be taken, the same could not be said for the region in general.
General Miramón, however, did not see the jungle in nearly the same manner. He recognized that with the Central forces largely ignoring the jungle itself - and even the inhabitants of the jungles - that he could use both to his advantage. So, he formulated his battle plans, in lieu with his own personal methods, with both things in mind: he would use the jungle-dwellers as scouts, allowing him access to all of the more hidden trails in the area, and attack Poras' supply lines and outlying positions from inside the jungles.
On September 7th, mere days before hearing of the defeats further south, Miramón's forces struck. By the 10th, his forces had closed off the Central supply lines, and forced Poras to send out forces in an attempt to re-open them. The force sent was cut down in the jungles. Three times this occurred, before Miramón's forces began their main assault upon the defense works, on the 18th. The tired - attacks from the jungles were making the defenders constantly on edge - and hungry defenders proved themselves to be no match.
On the 19th, even Porras, inept as he was, could see the writing on the wall - his position now being untenable - and began to pull his forces out of the town towards the southeast, and safety. Poras and his forces would be harassed the entire way to the relative safety of the ruins of Machaquila, arriving on the 3rd of October.
Here, Miramón had to stop and allow for supplies to catch up with his forces. By the time he was ready to again resume his advance in early December, news of the battles to the south, and the response of the Prime Minister back in Mexico City, had arrived: General Miramón, having been overly successful where his counterpart to the south had failed, was to be moved there, and the disgraced General Salas would replace him on the northern front. While a good move in the south, this would also mean that the northern front would largely remain static for the rest of the war.
General Porras would be demoted, and sent to Nicaragua to keep an eye on British forces in their Mosquito territories.
The arrival of General Miramón at the Mexican camp northwest of Huehuetenango in mid-January signaled the end of the city. While General Cañas was a fairly good general at his style of warfare, and was able to best General Salas, Miramón was an entirely different animal.
As in the Battle of Flores, Miramón went after the Central supply lines. While not nearly so effective here, given that the terrain was more open, the tactics still caused many difficulties. The larger army he had only made this easier. When the assault on the defense works came about in June, it stood little chance. General Cañas was forced to pull his forces out of the area, retreating southwards through the mountains to the city of Quetzaltenango.
Here, his defensive position was even better than at Huehuetenango. As a result, General Miramón had to stop his advance to get more reinforcements and artillery.
However, that did not mean that he had to halt operations. While to defeat the United Provinces meant that the Mexican Army had to advance through the highlands and jungles, it was not the only area that they could be hurt.
The coastal regions were such an area. The Mexican Army had not occupied them, though they could have advanced had they chose to do so - the logic here was that, correctly, the Central Americans would attack the rear of the advancing troops and wipe them out. As a result, they were only being blockaded, after a fashion. Yet, they were sparsely defended - a perfect target for raiding.
General Miramón's plan was to take advantage of this. Assembling a few of his cavalry regiments, which in the mountains were of little use, he went west, and then south, from his headquarters, until they arrived at the coast.
After receiving supplies, he turned to the east. In communication, though slow, with his forces, he was able to both conduct his raid and keep an eye on preparations.
November found his units south of the entrance to the main pass that if he went north, would take him to Guatemala City. However, he found it to be extremely well defended - the Centrals had been worried about assaults by Mexican Marines, so they had ensured the city would be safe.
So, he continued to the east. January of 1859 saw them in the province of El Salvador, pillaging and looting. On January 26th, they arrived at a pass west of the Salvadoran capital, and found it only lightly defended. By February, he had arrived in San Salvador, and his forces had begun to pillage and loot the Salvadoran capital.
However, this was as far as he would go. Word of preparations nearing completion further west at his headquarters arrived at almost the same time as reports from his scouts to the north of the city that an army was almost there from the Central capital at Tegucigalpa. Within hours, he had his forces on the move southwards. In March, they would be picked up by vessels of the Mexican Navy, and carted back to the west, disembarking at Tapachula, and arriving back at headquarters in early May.
Battle of Quetzaltenango
After resting for a month, General Miramón launched his offensive on Quetzaltenango in mid-June. Given the area, he could not launch an attack as at Flores or the second battle of Huehuetenango - he had to launch a more conventional assault.
From his headquarters, and the main base camp, north of the town of San Francisco El Alto, Miramón launched a small attack. Here he also concentrated his artillery, for this was also the main area of Central defenses - and the entryway to both the city, and the road to Guatemala City itself laid behind them. However, he did not concentrate his attack here, as it was so heavily defended and he did not expect to break through them.
His main attack, with two prongs, was to the west. One prong went south from the town of San Carlos Sija, and the other east from the town of Ostuncalco. In this, his goal - outnumbering Central forces overall by about three to one - was to attack all at once, and remove their ability with interior lines to reinforce themselves to counter his moves. While his forces would suffer casualties, it was fairly obvious it would work.
Both prongs managed to achieve their objectives. Central reserves had to be held in reserve, largely, because of the importance of keeping the only roads out of the area capable of holding the army in any retreat - south of the main Mexican camp - under their control. By late July, the two prongs had met up in the center of Quetzaltenango, forcing a general retreat by Central troops. With this in mind, General Miramón launched an attack towards the town of Salcajá, aiming to cut off the retreating Central forces from their main avenue of retreat. With the defenses being weakened as they pulled out of the area, his forces began to make progress.
General Cañas, fighting an exceptionally skilled retreat, and his forces, were able to slow them down enough, however. By the time the Mexican Army took Salcajá, both the General and most of his army had made it through the bottleneck. Still, some two thousand Central troops were cut off from this route - all but two hundred or so were taken prisoner.
Unlike last time, however, Cañas was unable to get as good of a defense line established after the battle. The area was not as good defensively, and more open. His well-organized retreat around Lago de Atitlán kept the Mexicans to slow advances for months, into the spring of 1860 - buying enough time for both Central diplomats to do their jobs, and for events in Asia to start to come to a close.
By April of 1860, events in Asia had more or less come to a close - Peking would fall by the end of July. As a result, American attention could be focused elsewhere. At the same time, efforts by Central diplomats in Washington, and news of the progress of the Mexican Army towards Guatemala City brought the war in Central America to the attention of the Fremont Administration.
Given Mexican ambitions, and their bitterness over their loss in the Mexican-American War, Mexican domination of Central America was not something that the American government could tolerate. And if they took the city, that would likely mean they could secure half of the sub-continent. This could not be tolerated. But, of course, they would not intervene for nothing. That the intervention would ensure the survival of their fellow republic would also sit well.
So, by April, President Fremont was finally willing and able to do something about it. With Congressional backing, he authorized the State Department to begin negotiations with Central American diplomats.
Given the state of affairs, they were authorized to give up a lot of things. Luckily for them, the American government agreed to intervene easier than they had expected - they would use naval squadrons to break the Mexican blockade of the coastline of the United Provinces, and use that and diplomatic positioning - understood to mean that they would threaten war if the Mexicans to not do it - to make the Mexican government withdraw and agree to peace.
In return, they asked relatively few things, which was seen as an admission of their desire for a weaker Mexican state. Foremost among their demands was the right to build a canal in Nicaragua, and some degree of control over a territory stretching for six miles on either side of the canal. They would around ninety percent of the profits from the canal, until its construction was paid off, after which it would revert to a more even split. American interests would also be granted trading rights throughout the Republic.
These terms were agreeable, and far better than they had been expecting. Within days, they had agreed to them.
Battle of the Bay Islands
In the Pacific, the American Navy had little trouble removing the weak blockade - the secondary status of the Pacific had meant there was almost no vessels on that Ocean - which would not be the case in the future. Most of the Mexican Navy would flee to neutral or friendly ports and remain there.
However, in the Atlantic, it was more difficult. The American squadron assigned the task, under the adventurer William Walker because of his knowledge of the region and made a temporary commodore for the task, faced a more modern and larger group of vessels. The Mexican Navy grouped its ships together, in order to force a battle so they could maintain the blockade. A pair of surviving Central Navy vessels attached themselves to the American squadron.
On June 8th, 1860, the two squadrons met in battle near the British Bay Islands, of the coast of Honduras. South of the island of Guanaja, the Mexican Squadron laid itself out in a line on a north-south axis. The American Navy, with the attached Central vessels, sailed straight for them, cutting through their lines with their forward guns, and curling around them. In doing so, most were damaged, heavily a one case. Using their superior numbers, the American Squadron surrounded the Mexican vessels and blasted them into surrender. By late afternoon, the battle was over. A single Mexican ship had been sunk, three had managed to flee northwards, and the remainder were forced to surrender.
As soon as word of the battle reached Washington, they sent a message to Mexico City: cease fighting, and retreat back to Mexico, or we will declare war.
Knowing that they would have lost, the Mexicans had no choice but to comply. Another week, and they would have been in the outskirts of Guatemala City.
Treaty of Philadelphia
The Mexicans and Central Americans met, with American negotiators, in Philadelphia, in August. With the position of the Mexican government made clear, they were forced to accept the independence of the Central Americans, and make some financial restitution - though not anywhere near a back-breaking amount. In exchange, the Central Americans would drop their claims to the state of Chiapas.
These were - grudgingly - agreed to by both parties, who signed the Treaty of Philadelphia on September 11th, 1860.
In 1862, as per the agreement, the American government began construction on the Nicaraguan Canal. It would be completed in 1872, three years after the Suez Canal. Revenues from the Canal would switch to being fifty-fifty in 1894, when its costs were entirely paid off.
For Mexico, the war marked the final turn away from the Americans in international diplomacy, begun decades earlier with the loss of Texas. Prime Minister Almonte also got blamed for the loss, and a liberal government under Benito Juárez came to power as a result.
For the United Provinces, it marked the start of a relationship with the United States that would eventually turn into an alliance.