The key seemed to be series of events that slipped by the mutual defenses and projections that each side has set up.

It's mutual defense against a common enemy - those snakes.

Every planter here was obligated by mutual defense to respond in such emergencies.

When the talks fell through and then leaked, some assumed both sides had been seeking mutual defense.

So the newly arrived white man found various tribes bound together over many generations, for mutual defense.

So the two species stay together because they provide a mutual defense.

That did maximize the mutual defense of his ships.

Military pilots use formations for mutual defense and concentration of firepower.

He was esteemed by his neighbors, but never mixed much with them except in times when they must unite for mutual defense.

In fact, the kingdoms merged from time to time for mutual defense.