Why did stalin and hitler become allies in the summer of 1939?

Whose writings were the source of the idea that people have a right to abolish and replace a government that violates their natural rights?

John locke viewed the social contract as a choice or "consent of the governed", where the people possess the power to change government. how did thomas hobbes see the social contract? man is born in chains, but can be set free through good deeds. man is born happy, but becomes more miserable as he ages. man is born poor, but can rely on other individuals for security. man is born selfish, but can give up some freedom in return for security provided by the government.

World war 2 was caused, in part, by which of these factors?