How many space marines AND assault ships would that be? And that's if there's no defending ground troops. Add to that a bunch of Militia and even ground attack defending ships.
I'm playing this game where the XSpec were very lucky with their starting conditions. 5 or 6 Ideal systems in their close vicinity, their pop just exploded. They spread their pop, but their systems are close to empty. 40~50 pop, 10~15 Militia, almost no structures. I'm taking them out, BUT, their Militia keep me from conquering their systems. I managed to conquer those with a couple of Militia, but the rest are not possible at this point (turn 70ish). A bit my fault too, I went more for air supremacy, with Destroyers, Corvettes, Merlins and Falcons. The Battlecruisers are coming, but so are their ground missiles.
Being more the diplomatic guy, i can't complain. I prefer to have 1 or 2 enemies and various allies.
The Order aren't supposed to be very diplomatic; and if it tanks your economy...