POD - Western Rome keeps Italy.
In 276, Rome was divided into the Western and Eastern Empire. In OTL, Western Rome died a painful death via barbarian invasion. However in ATL, the Western Roman Empire keeps its territory in Italy, Sicily, Corsica, and Sardinia. In 517, the Pope became the emperor of the Western Roman Empire, and the WRE became the Papal States of Western Rome, or PSWR.
In the East, the Byzantines continued to grow after 276 until the 6th century, when African tribes conquered Egypt and Cyrene. The Byzantines conquered Ukraine, the Caucasus, and Romania by 750.
The Glorious Arabian Kingdom
Mohammad is never born. Instead, during the early 600s, the Arabian Kingdom grows into great proportions. In 623, the Pope crowns the king of Arabia an emperor. In 630, the Arabs invaded Syria and Mesopotamia, creating Christian states there. The Persians began to lose their land in the Middle East ... for now. From 630-74, the Arabs occupied most of the Middle East, until 674 when the Persians retook Mesopotamia.
The Arabs are most known for their construction of the Suez Canal in 651, which opened up trade between Christians and Chinese without having to deal with vicious Hindu and Zoroastrian warlords in the Far East.
The Zoroastrian empire of Persia waged war with Arabia in 674, taking back Mesopotamia. In 690, Syria and East Anatolia became Persian protectorates also.
The Persians besieged Constantinople in 711, thus ending the Byzantine Empire but creating the Persia Empire under the King Farso. Greece and Bulgaria fell also to Persia.
711 through 1456 are known as the Middle Ages, because they are between the Modern and Ancient times. It wasn't a time of technological advancement, but it wasn't a dark age. Throughout that time, the Zoroastrians spread their influence into Poland and Ukraine, while the Catholic Church split into the Roman Church (Italy, Africa), the Belgican Church (Belgium, France) and the Anglican Church (England).
Also in 1040 the PSWR dissolved into the Kingdom of Italy (north, south Italy and Sicily, Sardinia, and Corsica) and the Papal States (central Italy).
Throughout the 1400s, gunpowder became mainstream and cannons and guns were more widely used. In 1456, German scientists invented the printing press, and in 1461 the steam engine. By the early 1500s, almost all of Christian Europe was connected by rail. This helped wars become much faster, as transportation was more efficient.
Age of Discovery
No Christopher Columbus was ever born, but in 1503, the Portuguese funded a voyage to the west which discovered Florida. Until 1517, the new land was a secret that only the Portuguese knew about, but in 1517 the English, French, Italians, and Germans discovered the new world as well, and in 1518 Netherlands and Spain.
Soon enough, Australia, Antarctica, South Africa, and Siberia was discovered. The European powers as well as Persia colonized the new land. In 1550, the Berlin Conference was held between Portugal, Spain, France, England, Netherlands, Belgium, Italy, Germany, Persia, and Russia to discuss the division of the new world. It resulted in Portugal getting most of OTL Gulf of Mexico and the Russians getting Siberia, while the Persians were given much of East and South Africa. Other states were given small prizes, which later grew.
First Age of Technology
As the Europeans colonized new places, they grew in population and economy, and railroads were built. In 1671, the world's coal supply was used up due to so many railroads. A short Age of Chaos ensued (1671-1710), where the United States, Bolivia, Australia, Austria, and Brazil seceded from their colonial masters to become independent but after that scientists invented new fuels, such as ethanol and water-fueled cars. From 1710-49, the First Age of Technology occurred, when scientists also invented such things as: electricity, telephones, radios, cars, nuclear bombs, and planes.
World War 1
Unfortunately such a great age had to end. In 1749, the new technologies were put to a test. Two alliances had formed in Europe over the past few years as the kings were afraid of the new war technologies. The alliances were the Free Powers (France, Germany, Netherlands, Spain, and Persia) and the Allied Powers (England, Italy, Portugal, Belgium, and Austria).
The war broke out in December of 1749. The Free Powers seemed to be winning at first, after they besieged Brussels and used nuclear bombs to destroy almost all of Austria. but the Italians and English used their massive air fleet to bomb the crap out of France and Germany, and by the end of 1751, the Russians signed an alliance with the Allies, so they sent about ten million soldiers to help the Allied Powers' effort.
Throughout 1752, 1753, and 1754, the Allied Powers won almost every battle. They bombed even more of France and Germany and occupied Spain, fighting heavy resistance. In 1755, all the Allied Powers either signed peace treaty with the Allied Powers or they were completely occupied. That is, all but Persia.
Beginning in 1755, the Allied Powers realized they would have to sooner or later fight the Persians directly. The Persians had about 30 million soldiers, a navy larger than any other, 500 nuclear missiles (compared to the rest of the world's 307 combined), and an air force that consisted of ten planes to the entire Allies 1.
The Allies launched an attack on the Bosporus in September, 1755, losing up to one million of their own men but killing only some 4,000. In early 1756 through 1757, the Allies recruited men in occupied Spain, France, and Germany in numbers of 15 million to fight on the front line with Persia. In November, 1757, the Persians finally surrendered after Trebzond was bombed with a nuke and the Persians lost about one-half of their population in Anatolia due to heavy bombardment. However, the Allies didn't get off scot-free ... they lost a lot of people as well.
During the war, over 190 million soldiers fought, and 70 million died. There were four billion people on earth at the beginning of the war, and one billion died during the war.
The Dark Ages
From 1757 to 1859, Europe and the rest of the world was in yet another dark age. Europe's colonies in Mexico, Columbia, Peru, Argentina, and New Zealand revolted, and no new technology was made.
Second Age of Technology
But in 1859, an Austrian scientist created penicillin, a drug to treat pneumonia, and Tetrazone, a drug to treat schizophrenia and bipolar disorder. Throughout 1859-61, the Austrian medical companies funded research worldwide, creating a medical renaissance. By 1862, this renaissance spread to other sciences, when tanks, tvs, the internet, stellar bombs (more powerful but more precise than nukes), the cure to AIDs, the cure to cancer, and refrigeration. The Second Age of Technology lasted until 1931.
In 1931, the scientific corporations of the world, mainly Teramati, Yemel and Kurbuns, were huge monopolies. Those three companies controlled up to one-third of the world's economy in 1931. They were spending large sums of money on new research that they believed would get them more money, but by 1931, the thinkers of the companies had no new ideas, and up to $500 billion was wasted that year, causing a small economic gap. The next year, another $750 billion was wasted. That gap caused a huge economic depression worldwide.
From 1931-47, the world was in an economic depression. There were many Communist revolutions, and the revolutionaries took power in the United States, France, Columbia, Peru, China, and most notably Japan. Also, new international trade laws were created so that (if the world recovered) this would not happen again.
World War 2
The only thing that ended the Great Depression was war. In 1947, the Communists of the world (but mostly the French, Americans, and Japanese) declared war on all of capitalism. They funded Communist revolutions worldwide, and used massive civilian armies to invade Germany, Spain, Benelux, and China through 1947. The Communists also used stellar bombs, which caused extreme damage to Eastern Europe that could not be recovered for the next 40 years. In 1949, the war turned around when the Spanish won the Battle of Granada and forged a counterattack to take back North Spain. Also in China, anti-Communists took Xiamen, and reconquered the north. In 1953, all of the world's Communists were defeated after capitalists bombed Paris, Tokyo, and Bordeaux with stellar bombs, killing up to 37 million people.
During the war, 420 million soldiers fought, and 221 million died. There were 7.8 billion people on earth at the beginning of the war, and between three and four billion died during the war (1-2 billion died after the war as a result of famine and revolts).
The Age of Prosperity
From 1953-62, the world's leaders held major conferences at Yalta (53-57), London (57), Granada (57-58), Havana (58), Sao Paulo (58), Helsinki (58-61), and Yalta (again, in 61-62) to discuss: -the division of Communist lands -the prevention of monopolies -the dissolution of nations that cause war -the banning of nuclear and stellar bombs -the unification of the world's states
In 1962, the leaders concluded one thing: the world would be united. The new global kingdom was called Catholic Rome (universal Rome, with its capital in, yes, Rome). From 1962-2297, a perfect age of the world was experienced. There was enough technology so people weren't in danger, but not too much that war and technological takeover killed millions of people.