Secret Wars was a 12 issue series from the mid 80's that was really good.  I think everyone will agree that the most significant event in Secret Wars was Spiderman finding and wearing the black Venom symbiote, although there were a few others that ranked up there.  

There is a cool Secret Wars website that has a bunch of really cool merchandise and issues.  If you are interested check it out.

Meanwhile, back in the real world, the Secret War was the fight in Laos against communists during the Vietnam War.  Apparently these actions were key in interrupting weapons and supplies getting to Vietnam, so it sound like good work by some brave guys.