There were many economy reasons for expanding. When you have more land you profit more. There would also more opportunity with more land.
Based on the order of occurrence, the government used by rome during its history is :
1. Monarchy ( 753 - 509 BC)
2. Republic (509 - 27 BC)
3. Oligarchy (27 BC - 476 AD)
4. Dictatorship
hope this helps
