Historically, the Soviet Union thought that the United States was planning something in Afghanistan and invaded because they were worried about 'terrorism'... Sound familiar? At any rate, it became their Vietnam, but worse.

Of course, America didn't even care about Afganistan until the Soviets invaded. They were still pursuing the policy of "anything the Soviets do must be worth pursuing" so they started funding the Mujahadeen and sending in stingers.