You can't complete this game without allies. But luckily it's pretty simple. Every mission contains enemy soldiers. To put it simply, you can't capture dead soldiers. Here is how to do it. First you must knock out the target you want to capture. Then drag him/her back to the truck (or nearest cardboard box later in the game) before he/she wakes up. After you complete or abort mission, he/she will appear in prison at Squad management- screen. When soldier is in prison, you can only look at their skills, remove their equipment, change their name and dispose them (if you're playing for the first time, don't get dispose them unless your absolutely sure). After few days he/she will join your unit, faster if you have Politician- career in your squad.