First of all... what period? because if you are talking about this time, I think it is becaise they want to feel powerful to be able to have more allied countries in any situation, they also do it because they want to control most of the world natural sources that other countries have.
Answer:
1. legislative branch- has a congress that makes laws
2. executive branch- led by a president who to carry out laws
3. judicial branch- has courts to interpret laws
