Because Richard Nixon, in his campaign for presidency promised Vietnamization to the American people, many felt betrayed when he had announced he was planning on invading Cambodia in April (before the Kent State shootings). People became angry and resentful which is why many protests and rallies became more widespread and intense. Because of the reaction to the looming Cambodia invasion, more than 250 State Department and foreign aid employees signed a letter to Secretary of State William Rogers, criticizing U.S. military involvement in Cambodia. Also, “there were a series of congressional resolutions and legislative initiatives that attempted to limit severely the executive war-making powers of the president.” (http://www.history.com/this-day-in-history/nixon-defends-invasion-of-cambodia) On December 29, 1970, Congress passed a modified version of the Cooper-Church Amendment (a bill that would have barred funds for future military operations in Cambodia which was voted down by the House), barring the introduction of U.S. ground troops in Laos or Thailand. In 1970, the North Vietnamese launched a large attack against South Vietnam called the Easter Offensive. The attack included invasions to destroy as many units of the ARVN (the Army of the Republic of Vietnam) as possible and also gain as much territory as possible. American troops succeeded in stopping the attacks eventually, after much damage to South Vietnam had been done. U.S. air power played an essential role in attempting to stop the attack. The attack had been successful for the North Vietnamese and caused more than 100,000 casualties of the ARVN.