The accident in the Tonkin Gulf when North Vietnamese forces attacked the U.S. vessels and caused two airplanes to crash was a good reason to start the conflict, as the troops of North Vietnam violated the Geneva Convention and attacked a foreign navy in the neutral international waters. The United States has to react on this accident, as it was the mater of international respect, but at the same time the presidents administration had to estimate the future consequences of the military strike back. It was not secret that a lot of Soviet weapon was concentrated in North Vietnam, and Viet Kong army was ready to start the war for the unification of the country as it was guaranteed to have a support from Soviets. Invention in Grenada was caused by the Cuban influence on Grenada's government in early 1980 iers. Grenada changed its political orientation and turned to the U.S.S.R. And Cuba as it considered them to be its partners. As the result it started to build its military defense system getting support from Cuba and Soviets. It was considered to be a threat to the security in the region that was guaranteed by the U.S.A. And the Organization of Eastern Caribbean states. As a result the U.S.A. started intervention of Island. More than eight thousand U.S. soldiers took part in the campaign, 19 died and 119 were wounded. Grenadeans lost 70 soldiers dead and 417 wounded. The cost of the campaign was 6 million dollars. As a result the government was changed to a more loyal one to the U.S.A. This case shows that sometimes the U.S.A. doesn't take the political and democratic freedoms of the definite countries where its interests are not met.

The policies Monroe doctrine that were later changed into the policy of F. Roosevelt of Pan-Americanism gave the United States nearly unlimited privileges in solving of different problems in any the region of the Western hemisphere....

These arguments completed ambitions of the U.S. monopolies in Latin America, and that's why any premise for intervention was exploited fully. Any kind of accidnet that had military origins and violated the U.S. Security in the countries of Latin America or other parts of the world was considered to be the attempt to the security of American state and this was that reflection and feedback in the eyes of American government and American presidents especially in the years of the Cold war. The fear of communism was the reason why president Johnson didn't objectively evaluate the situation in Indo-China and the fear of communism took a dominant role in the foreign policy orientation of president Reagan. He used different reasons to show that America can defend it's interests and especially principles of "liberty and democracy," forgetting that they violated the freedoms of the sovreign nations. The stereotypes of "communist fear" had been coltivated in the western societies for decades and they become very difficult to be avoided when one comes to power. Nowadays when the "red threat" had disappeared with the collapse of the Soviet Union, a new threat has taken its place. it's international terrorism and religious Muslim fundamentalism.And the stereotypes that originate nowadays when the world community is fighting against terrorism, will result additional obstacles in percieving of different problems objectively.
Reference:

John J. Johnson, a Hemisphere Apart: Foundations of U.S. Policy toward Latin America Westview Press; 2nd edition (January, 2001)

Alonso Aguilar, Pan-Americanism from Monroe to the Present Monthly Review Pr (June 1, 1969)