[zaphirplane]

This may be where intuition and cosmic scale don’t align. The Milky Way is very old and is ~100k light years in diameter.

Say you are a few million year old civilization and you detect radio from a civilization 100k light years away takes 500k years for you fleeting arrive. You are still millions of years ahead in technology. If you are a stagnant civilization you probably stay home cause the other side would overtake you, but then again that motivation to get to them as early as possible. In any event presumably as your fleet get closer you would have a better idea of the technology difference and can just do a U turn

[ncmncm]

Civilizations that come into contact will tend to be those that are closer together, particularly if they make any effort to be inconspicuous.

The longer they go without contact, the wider their reach, and the greater their odds of contact.

We might suppose that the technology necessary to obliterate another civilization is arrived at early, and is hard to counter despite long subsequent development. Alternatively, civilizations that succeed in suppressing weaker ones eventually meet their match.