Terran Defense Force
The Terran Defense Force was created near the end of the unification wars, when victory for Ithaca and it's allies was certain. As the military branch of the Terra II planetary government, it is their duty to protect Terra II from threats, internal or external.
The TDF is currently trying to eliminate the threat of the Fire Legion. They put Shima Industries under their control to prevent any other Elemental Machines from revolting, as well as getting more warpower. When the Yoma start attacking, they have to enter into a uneasy alliance with the Fire Legion to defeat them.