Mr. Arzu will be the fourth civilian to assume the presidency since the Guatemalan armed forces relinquished formal control of the Government in 1985.
Behind the national security claim is the intimation that the Guatemalan forces are fighting Cuban-inspired Communism - keeping it away from the Rio Grande.
Appended to the letter is a list of dozens of horrifying atrocities by the Guatemalan forces.
Over the last decade, Guatemalan forces have been trained primarily by Israeli and Taiwanese advisers.
Although the outlines of American support for Guatemala's military have been well known, the nine-volume report confirms that the Central Intelligence Agency aided Guatemalan forces.
In the 1980's, Guatemalan military forces carried out a relentless campaign against rebels among the Indians who make up a majority of the country's population.
In 1988-89, the Bush administration strengthened ties with the Guatemalan armed forces.
After leaving school, she worked as an activist campaigning against human rights violations committed by the Guatemalan armed forces during the country's civil war, which lasted from 1960 to 1996.
The Salvadoran, Nicaraguan, Honduran and Guatemalan forces more than doubled in size between 1981 and 1986.
At the lake, he was joined by a reinforcement of 130 men, and routed the Salvadoran and Guatemalan forces.