Why did Rome first intervene in southern Gaul during the 2nd century BCE?

In the 2nd century BCE, Rome first intervened in southern Gaul primarily to protect the vital land route connecting Italy to its newly acquired possessions in Spain.12

This intervention was initiated on behalf of Massilia, a Greek colony and Roman ally, which was engaged in a struggle against the local tribes of the hinterland. By 121 BCE, these military efforts led to the formal establishment of a Roman territory known as "the Province" (Provincia, the origin of the name Provence), which spanned from the Mediterranean coast to Lake Geneva.123