The expansion of Roman territory during the era of the Republic made Rome a huge power and allowed it to take control of vast areas of land surrounding the Mediterranean. However, the expansion also led to stresses that destroyed the Republic and helped turn it into an empire.
During the era of the Republic, Rome came to dominate its area of the world. It defeated its major rivals, most notably Carthage. It also took control of areas as far as Syria in the east and what is now France in the west. This made Rome the greatest power of its time.
This expansion, however, helped lead to the fall of the Republic. The stresses of war made it very difficult for the Senate to effectively rule. This was exacerbated by the fact that the Senate was now required to rule a much greater amount of territory.
In these ways, the expansion contributed to the greatness and power of Rome, but it also helped lead to the collapse of the Republic.