[quote=darkwolf687]
Quite simply put, a nation which has lower technological prowess, military strength and/or economic power when compared to the other nations, or nations which would be relatively easy to defeat compared to the other nations in the galaxyGiven there's a fair amount of anti-matter floating around, the Valkian military could be considered this as they don't use shielding, meaning anti-matter bombs and anti-matter beams would be very, very threatening to them and until such a time they integrate shields into their ships, they would have difficulty stopping such an aggressor (Though even with shielding stopping anti-matter weapons is not an easy task for any one, I would assume)
[/quote]

You treat AM missiles like any other missile weaponry: you shoot them down, intercept them with your own missiles or move out of the way. The last option is a little finicky, because like nuclear weapons, AM missiles are AoE weapons.

You defeat AM beam weaponry by preventing the anti-particles from making contact with your ship. You might try an electromagnetic field, a large particle barrier that engulfs your spacecraft or a plasma shield. If you can tank particle beams and nuclear weapons, you can weather AM weaponry.

Powerful? Yes. Does it allow you to steamroll 'low tier nations'? No.