There were many factors that allowed the Byzantine Empire to last a 1000 years after the end of the Roman Empire which include the fact that Constantinople, the capital of the Byzantine Empire, was protected with walls that lasted almost the entire 1000 years, making Constantinople, and the center of the empire's economy/culture impervious to invaders.
The Treaty of Versailles was very harsh on Germany and promoted the rise of Nazism which was very aggresive and put other nations in threat.
The Treaty of Versailles demanded Germany to accept the war guilt clause, and the civilians were discontent about the government accepting the great humiliation towards Germany. They desired a stronger government that can return their national sovereignty and bring them national glory. This gave rise to Hitler who promised to bring national glory to Germany.
The Treaty also demanded a compensation of 6.6 Billion,as well as losing all colonies and had to cede territories. This caused Germany’s to suffer from economic collapse,and hyperinflation had caused civilians lives to be harsh. Many lost their jobs as well. The civilians thought the government at the time,Weimar Republic was weak and unable to solve the problems hence wished for a stronger leader. This again contributed to the rise of Hitler.
As Nazism rise, the nation adopted an expansionism policy hence actively invading other nations. It was until Germany set it's hand on Czechoslovakia that Britain and Frace decide it can no longer be tolerated,thus WWII broke out.
Hope it helps!
