Welcome
I guess until you doesn't destroy some of their ships, it should be ok.
War can be started by:
1. Destroying their ships
2. Landing ground units/attacking their planet
3. Colonising a planet in a system under their control (They won't attack at first, but it will deteriorate their opinion about you)
4. Using active sensors around their planets/ships too much (It may take a while until they attack because of this, so don't worry)