Macedonian Empire Post-Alexander
Upon Alexander the Great's death in 323 BC Hephaestion was crowned Emperor of Macedonia. Emperor Hephaestion immediately began a campaign westward to conquer the Roman Republic and Carthaginian Empire. Rome fell in 319 AD and Carthage in 316 AD, and he would be remembered as Hephaestion the Conqueror. Hephaestion died in 314 AD to be succeeded by his son, Aeropus.
During Aeropus' reign the Macedonian Empire invaded and conquered the Iberian Peninsula, the south of OTL France, and Africa out to the Atlantic Ocean to the west of what was the Carthaginian Empire. Aeropus helped stabilize the empire. His policies perpetuated a unified Macedonian identity throughout the empire.
Over the next few centuries the Macedon Empire would expand, taking the Arabian Peninsula, and sometimes extending further north in Europe. They extended into Central Asia around 250 BC and then into India around 125 BC. Around 10 BC Indian rebels gradually regained control. During this time lands in Central Asia at times change hands with various Scythian kingdoms.
Viking culture emerges and continues to dominate in Scandinavia, Iceland, and Greenland into the 2nd millennium. The Vikings also hold on to Vinnland in America, expanding into the powerful Vinnish Empire.
The Mongol Empire begins in 1206 when Genghis Khan unites the tribes of Mongolia.
Attempted Invasion of the Macedonian Empire
In 1219, as part of the Mongol Empires broader campaign, it invades the Macedonian Empire, which at this time controls territory from Persia to Spain, northern Africa, territory along the coast of the Red Sea running down to its border with Aksum, the Caucasus and the Black Sea, and territory going up to OTL France and most of OTL Germany. The unified Macedonian Empire is better able to fight off the Mongols, the war ending in 1223 with no loss of territory. The Mongols move on and as a result are better able to hold on to other territories.
Mongol Empire Post-Invasion
The Mongol Empire conquered all of Asia with the exception of the far north, southeast Asia, India, and the Macedonian Empire. With a smaller, more easily manageable empire the Mongols consolidate their hold.
The Macedonian Empire fearing its safety begins a military buildup after the failed Mongol invasion, and starts an alliance with the several independent states in Scandinavia and Germannia, the Indian Empire, and several Southeast Asian states. All boys are given military training from the age of 8 starting in this period.
Invasion of Japan
In 1298, after several failed attempts at conquering Japan, the Mongol Empire invades it. After 3 years Japan is successfully conquered.
Discovery of America
The Mongol Empire hearing of the Vinnish Empire on another continent sends an expedition east to find it. Several expeditions into the Pacific are undertaken and in 1311 Mongols land in Alaska. The Mongol Empire quickly conquers Alaska.