Tactics is a very deep, involved game. Chapter 1 merely sets the stage-for all intents and purposes, everything you do in Chapter 1 doesn't actually matter (except that you get some decent characters for when the battles get harder). Some of the events of Chapter 1 will come back to haunt you later on in the game, though.

Tactics is a tremendous story that looks back in on events that you caused/were there for and uses that rich stage as a backdrop for what happens next.