In my campaign, I wrote brief char backgrounds - nothing too clever or in-depth but enough of a skeleton for the players to then flesh out themselves with the help of events.
one player was an ex-con and was wholly self-motivated, another had a deep hatred of the Russians, there was a genial philosphical Canadian, an undercover Israeli, a Brit SBS with a sense of inadequacy. Basically, they all had very different motivations and had lots of trouble trying to work out what the hell they 'wanted'. Eventually they got bliss when they set up a base in Grenada where they presently are relaxing awaiting their next mission
One thing I have just thought of is one player was Black/Afro-caribbean origins and this caused all sorts of problems for the group whenever trying to be undercover or generally be un-noticed in the original camapaign zones. I am no expert but I was pretty sure that in Poland beyond NATO lines, 99% of the locals and WP forces would be white (maybe some Soviet troops of Asian origins).