Short Answer 
The U.S. intervened in Guatemala to contain communism, leading to the overthrow of President Jacobo Árbenz and establishing a military dictatorship. This resulted in significant instability, a civil war, and humanitarian crises, particularly the genocide of the Mayan people, leaving deep scars on the population.
Step 1: Understanding the U.S. Involvement
The involvement of the United States in Guatemala was primarily driven by the desire to contain communism in Latin America. In the early 1950s, the U.S. government viewed the democratically elected government of President Jacobo Árbenz as a communist threat. Consequently, they orchestrated a coup to overthrow his administration, believing this action would curb the spread of communism in the region.
Step 2: Consequences of the Coup
The aftermath of the U.S.-led coup resulted in significant negative transformations for Guatemala. The country transitioned from a democratic government to a military dictatorship, leading to a series of authoritarian regimes. Furthermore, this political instability ignited a civil war, which had devastating effects on the country and its citizens.
Step 3: Humanitarian Impact
The civil war that ensued produced severe humanitarian consequences, notably the genocide of the Mayan people. As the military dictatorship sought to eliminate perceived threats, Mayan communities faced violence, displacement, and systemic oppression. These events highlight the tragic consequences of foreign intervention, burdening the Guatemalan population with lasting scars and trauma.