'Instead of improving the situation, the US military became caught themselves in Lebanon's intensifying civil war...'
The October attacks were not the first - there had already been one major attack against US interests in the previous April, when 63 people were killed in a bombing of the US embassy in West Beirut. The US troops had initially gone in to Beirut, capital city of Lebanon, to bring some calm to the region - following the massacre, in September 1982, of hundreds of Palestinian civilians in the Sabra and Shatila refugee camps by Lebanese Christian militiamen. Instead of improving the situation, the US military became caught themselves in Lebanon's intensifying civil war, and were exposed to the growing anger of Lebanese Muslims with America's support for their Christian dominated government, and with American efforts to persuade the Lebanese government to negotiate a peace treaty with Israel.
The attacks did not themselves immediately trigger the withdrawal of the American peace-keeping force from Beirut. Troops stayed in the city until February 1984, with President Reagan insisting that they still had an important job to do. Nonetheless, the attacks undermined the conviction behind Reagan's policy, and weakened political support in the United States. In addition, Shi'ite Muslim terrorists resorted to the murder and kidnapping of American citizens in Lebanon. Eventually one of these kidnappings proved to be the last straw, and led to Reagan reversing his position and pulling American troops out of Beirut.