To cross the width of space, their technology must be far ahead of ours. Imagine a modern army fighting one from the 18th century, and you could imagine what a tank, a machinegun, modern artillery or whatever other aspects would do.
BUT: There is also the point that we would fight locally, while they would need quite long-winded logistics.
In regards to the long winded logostics (I read this from a second hand account and I’m sure this idea is from some scifi book) -a really fun idea is that if the aliens would send a war fleet our way and it takes say 50 years to get here… it is reasonable to assume that in those 50 years the aliens will do some technological breakthrough in both drive and weapon departments that by the time the fleet would get here a more advanced fleet would already be fighting the war - possibly even already won.
I think the idea can be found in Ender’s Game. As the story progresses further into enemy territory, he ‘controls’ ships which are increasingly outdated because those are from older fleets sent decades ago.
In regards to the long winded logostics (I read this from a second hand account and I’m sure this idea is from some scifi book) -a really fun idea is that if the aliens would send a war fleet our way and it takes say 50 years to get here… it is reasonable to assume that in those 50 years the aliens will do some technological breakthrough in both drive and weapon departments that by the time the fleet would get here a more advanced fleet would already be fighting the war - possibly even already won.
I think the idea can be found in Ender’s Game. As the story progresses further into enemy territory, he ‘controls’ ships which are increasingly outdated because those are from older fleets sent decades ago.