Modern international law recognizes only three lawful justifications for waging war: self-defense, defense of an ally required by the terms of a treaty, and approval by the United Nations.
The Europeans were exposed to new technologies, inventions, and ideas as well as old ones that had been lost and forgotten in Europe for centuries. The arrival of Muslim innovations in medicine and science helped Europeans catch up to the rest of the world. Politically, many leaders left Europe to focus on the crusades and were unable to respond to uprisings in their homeland or appointed others to rule in their absence. The crusades eroded the power of the feudal aristocracy and elevated the role of kings. The Papacy became more powerful and it's church became much wealthier. International trade increased and there was a new demand for foreign goods. It also reawakened Europe's curiosity, driving them to discover and explore new places, create new inventions, and innovate new ideas.
Corruption of the Russian Monarchy, Low resources during WW1, and public opinion.
I think that it is a<span> shift from an agrarian economy to a manufacturing economy</span>
