Suppose that there are 2 interstellar empires at war with one another, both armed with FTL drives which cannot be used within a certain radius of huge gravity fields, stars, gas giants, etc. Another thing to note is that both empires use the same FTL tech, which they had both independently researched, as it was the Apex Technology or something.
So the 2 empires will be at war with one another. On their first battle against one another, they stand off against one another from millions of miles away shooting with their cannons. Suddenly, one of the ships from one side suffers a critical hit, and detonates, wiping out both fleets, turning the local planets to plasma, and solidifies the local star by fusing all the helium into lead all in a flash. The blast then rippled outwards, FTL and completely irradiates all systems in a large(25 parsecs) radius. Now, both empires now know the extreme power of the explosion when their FTL ships explode, and they decide that they don't want to fight ship against ship anymore, but they are still at odds with one another and want to fight.
So, that is a bit of the setting, now for the actual question. How would 2 interstellar empires fight in space if they are both extremely unwilling to blow each other's ships up
- There is FTL, and is outfitted to most Cruiser and above sized ships.
- Both empires want to fight, but they don't want to blow up each other's big ships. The ships can be attacked on small scale and boarded and neutralized that way.
- Both empires had never actually seen the FTL drive explode like that, but quickly deduce that such an occurrence would be very common if they kept fighting like that.
- Between the 2 empires, they probably easily lost a dozen or so systems from the first contact
- Take note that the huge explosion is caused by huge chain reactions from the FTL drives of both fleets, and the local civilian ships as well.
- A single lone ship detonating it's FTL drive would be still be enough to wipe out a large portion of a single star system, but it would easily also trigger any other FTL ship in the system.
- MAD would probably not be in play, not until one empire is beaten all the way to their home world, as the detonation would have very real consequences.
HUGE NOTE: This question is more about how 2 empires would fight, not about how to weaponize the FTL drive.