Let's take this further with a thought I always like to spend time musing on from time to time:

If we discover alient life within our galaxy, and years pass and we become friendly. What if another galaxy attacks ours, and we fight them.

Galaxy vs. Galaxy.

One side wins, the other falls in line and is absorbed in their ways. The we form one huge 'quadrant' in space.

Another quadrant attacks us ad infinity.

When does the tribal, us vs. they end? -Does- it end?