• A group in a nation calls for help and another nation joins in to help them. Can be a military (martines during punic war) or an ‘ethnicity being genocided’ (russo-ukraine)
  • You’re a dictator and you’re running a risk of being overthrown, so you start a war bc if you win you’ll be popular (falkan war, japan v russia)
  • Economic gain (japan ww2 to get natural resources)
  • religious difference? (crusades)
  • Being excessively taxed by a foreign power? (american revolution)
  • Widespread poverty, wealth, dictatorship (russian revolution - basically civil war, french rev), massive differences in culture/economy within a country (american civil war, south wanting slaves + to succeed, north not + wanting to maintain union)