I believe the answer is Checks and balances. Check and balances is created in order to prevent the government from becoming too powerful and transformed into a tyrant. By giving both Congress and the President the power to limit each other, none of them could fully create Regulations without additional support from the citizens.
Mutual defense alliances was a significant cause for starting World War I. Basically, what happened was all of the countries were somehow alliances with other countries. Conflict between different countries caused the allied countries to be involved which eventually led to World War I.
