Complex sentence: The first was used when the Celtic Helvetii were forced to evacuate their homes in Southern Germany and Switzerland due to incursions of unfriendly Germanic tribes to add incentive to the march, the Helvetii destroyed everything they could not bring.
Split into simpler sentences: The first was used when the Celtic Helvetii were forced to evacuate their homes in Southern Germany and Switzerland due to incursions of unfriendly Germanic tribes. To add incentive to the march, the Helvetii destroyed everything they could not bring.