See I don't think we would resist, at least not in the long run. Initially we'd be like "Go away and leave us alone, we don't want to be part of you Imperium." (maybe, some nations would probably be more like "Yes, oh great and glorious space men. We Believe!") That would all change however the moment the Imperium decided to play rough. Orbital strikes at the White House, maybe the Eiffel tower and other such monuments, they don't even have to kill anything (though they will). And if the governments don't fold the people will. After all, it's not likely the Imperium's gonna come in all "Bow and be our slaves." more likely is the approach we see in the HH novels "Rejoice brothers, you are alone no longer. Come, join us in glorious illumination." People are gonna eat that up, especially if the alternative is fiery death.We would lose, we might inflict substantially more casualties on them than they us, but that won't matter. We would put up one hell of a fight, sure, but we would be screwed from the word go.