Two Galaxies Cannot Be At War

There are plenty of stories involving war.  War can exist in several forms: nation against nation, brother against brother, family against family, race against race.  However, no matter the variation, there is a limit.  The lands involved cannot be too big.

Suppose two cities are at war.  One city sends its army into the other city, then kills everyone it sees.  They can systematically enter every building and check them for people.

If two nations are at war, it can work similarly, though it would take longer for armies to systematically conquer each city as they make their way to the capital.  But it can be more difficult to be so thorough.  Imagine invading a country like America.  It is so massive that it is nearly impossible to get everybody.  There are countless places that people could hide in, both in a given city and out in the middle of nowhere.  It would take decades to even check all the land for people in hiding.

How much larger can we get?  Can two planets be at war?  Maybe.  Maybe if there were weapons at work that could destroy areas the size of large cities.  But at that point, the human factor is pretty inconsequential.  When millions of people can be taken out in a single shot, they become nothing more than a statistic.

Two galaxies cannot be at war.  This is a definite extreme.  The sheer size of a galaxy is incomprehensible.  Humans are no better than a speck of dirt in that scope.  In order for humans to matter whatsoever, the galaxies in question would have to be relegated to an area not much larger than a small country, which would negate the reality of galactic warfare.

Stories are always about people.  Whatever is going on, people are involved (or something anthropomorphic).  If you cover too large of an area, it can never be about people becuse you will be too zoomed out to see them.