Why did the United States become involved in the Soviet-Afghan War?

The United States wanted access to the Afghan oil fields.
The United States wanted to retaliate against the Soviet boycott of the 1984 Olympics in Los Angeles.
Representative Charlie Wilson convinced Congress to fund Afghan resistance to Soviet influence.
President Ronald Reagan wanted to force the Soviets to withdraw from Afghanistan.

The United States became involved in the Soviet-Afghan War because Representative Charlie Wilson convinced Congress to fund Afghan resistance to Soviet influence.

Explanation:

Motivated by the possibility of causing a setback to the Soviet Union, Wilson had as a Representative a significant role in the conduct of Operation Cyclone, aimed at funding the mujahideen fighters that faced the Soviet Union in its invasion to Afghanistan

In the summer of 1980, Charlie Wilson read a press release describing how hundreds of thousands of Afghan refugees fled their country. However, few paid attention to this situation, including the US government itself.

Wilson contacted a member of the Congressional Finance Committee who dealt with CIA secret funds and asked to double the budget for military operations in Afghanistan. A short time before, Wilson had been appointed a member of the Defense budget committee, where nine members from the House of Representatives were responsible for funds from CIA secret operations. This placed him in an influential position to impose his views, supported by the American consul in Pakistan, Joanne Herring.