China, a History

Arguably, the biggest factor that led to the downfall of Sui Dynasty was the series of massive expeditions into the Korean Peninsula to invade Goguryeo, one of the Three Kingdoms of Korea. The war that conscripted the most soldiers was caused by Sui Yangdi. The army was so enormous it was actually recorded in historical texts that it took 30 days for all the armies to exit their last rallying point near Shanhaiguan before invading Korea; in one instance, the soldiers--both conscripted and paid-- listed over 3000 warships, 1.15 million infantry, 50,000 cavalry, 5000 artillery, and more. There were just as many supporting laborers, and an exorbitant military budget that included mounds of equipment and rations (most of which never reached the Chinese avant-guard, as they were captured by Goguryeo armies already). The army stretched to "1000 lis (a Chinese unit of length, in modern translation one half-kilometer, though its precision in antiquity may be questioned), or about 410 kilometers, across rivers and valleys, over mountains and hills."

In all 4 main campaigns, the military conquest ended in failure. Nearly all the Chinese soldiers were defeated by the prominent army leader Eulji Mundeok of Goguryeo. For example, of the 305,000 Chinese troops, only 2,700 returned to China, according to the Book of Tang records, soldiers in summer conquests would return several years later, barely living through the cold and famishing winter. Many died of frostbite and hunger.