First of all, your analogy is absurd; an Afghanistan army never invaded Europe or any American Ally. The motivation guiding US involvement in Afghanistan evolved from the Cold War and the fear of an expanding Soviet influence to corporate oil and gas interests. In 1978, Afghan Communists came to power and the following year the Soviets invaded Afghanistan and established a puppet regime.

In 1980, Carter authorized the CIA to funnel money to the Afghan rebels through Pakistan's Inter-Services Intelligence. In 1981, Congress approved $1.6 million in assistance to Pakistan that got funneled through Pakistan Intelligence to aid the Afghan rebels. In 1986, Congress approved a deal to send 300 anti-aircraft missiles to the Afghan rebels and provide combat training. The CIA instructed Pakistan Intelligence to recruit Muslims to fight as rebels. Bin Laden, financed by the his father and the CIA, built a training center in Afghan and in 1989, the Soviets withdrew from Afghanistan and Bin Laden set up the Al-Qaeda Network.

In 1995, the State Department NSA and the CIA formed a group to study U.S. oil and gas interests in Caspian region and Turkmenistan officials met with U.S. based Unocal Oil in Texas to discuss construction of gas pipeline from Turkmenistan to Pakistan thru Afghan. A deal was signed for an Afghan pipeline agreement with Unocal and the Saudi Arabian Delta Oil Company. The Taleban got greedy and the pipeline deal fell through. The US decided to invade Afghanistan to overthrow the Taleban before 911.

As is most always the case, the US has used its Armed Forces to protect Corporate interests around the world. Since you constantly question my sources, do your own research to verify the information in my post. It's all true. Here's a link to the BBC to get you started http://news.bbc.co.uk/1/hi/world/south_asia/1550366.stm