Two of the chief tribes were the AEDUI and SEQUANI.

The former had been taken under the protection of Rome; the latter, impatient of control and Roman influence, had invited a tribe of Germans under Ariovistus to come into Gaul and settle, and be their allies.

These Germans had attacked and conquered the Aeduans, taken from them hostages, and with the Sequanians were in the ascendency.
In Switzerland lived the HELVETII.

They had so increased in numbers that their country was too small for them.

They therefore proposed to emigrate farther into Gaul, and the Sequanians, whose lands bordered on those of the Helvetians, gave them permission to march through their country.
Such was the state of affairs when Caesar arrived in Gaul.