|How many men can some of the larger nations draft and arm to resist an invasion? China, US, Russia, India, EU all seem to be capapble of putting up quite a fight, and any invasion would likely be highly disadvantaged numbers wise. Its really hard to take enough soldiers from your planet to attack one lightyears away that can arm 100 million plus soldiers.
So first off, how many soldiers does the world have in its armed forces right now while we are mostly all at peace? Secondly, how many could we equip to fight? Although there hasnt been another world war to show us the Earth's industrial might, we must have at least doubled what we were capable of producing during the 40's right? The US in its 4 years of total war in WW2 built close to 300,000 combat aircraft. Granted, planes have gotten more complicated and more expensive, but their capability's have also taken a quantum leap.
Would we win with sheer numbers alone if we united to defend our planet?