Why did the roman republic collapse?

Rome declined for a variety of reasons. First, they had grown too large to effectively govern. Rome was also suffering from considerable internal pressures. There were so many religions within the borders that it was hard to feel a sense of unity with your fellow citizens. There were also several times the Black Plague killed significant numbers within the Empire; because of this Rome was forced to rely on outsiders for maintaining it's military might. These barbarians demanded more and more benefits in order to keep their loyalty. Rome had also developed a significant welfare state, where every citizen was entitled to at least some free food every day, publics baths, etc. Large amounts of the Imperial treasury were dedicated to maintaining the armies and the corn/bread dole for the people. This left little money in case of an emergency. Outside the Empire there was an increased number of migrating people fleeing into Roman territory, often violently, trying to find a better life for themselves.