Presidential Republic (1925–1973) in the context of Salvador Allende

Augusto José Ramón Pinochet Ugarte (25 November 1915 – 10 December 2006) was a Chilean military officer and politician who was the President of Chile from 1973 to 1990. From 1973 to 1981, he was the leader of the military junta, which in 1974 declared him President of Chile; in 1980, a referendum approved a new constitution confirming him in the office, after which he served as de jure president from 1981 to 1990. His time in office remains the longest of any Chilean ruler.

Augusto Pinochet rose through the ranks of the Chilean Army to become General Chief of Staff in early 1972 before being appointed its Commander-in-Chief on 23 August 1973 by President Salvador Allende. On 11 September 1973, Pinochet seized power in Chile in a military coup. The military had previously received financial and intelligence support from the United States, which favored the military coup that toppled Allende's democratically elected socialist Unidad Popular government and ended civilian rule. In December 1974, the ruling military junta appointed Pinochet Supreme Head of the nation by joint decree, although without the support of one of the coup's instigators, Air Force General Gustavo Leigh.

The military dictatorship of Chile led by General Augusto Pinochet ended on 11 March 1990 and was replaced by a democratically elected government. The transition period lasted roughly two years, although some aspects of the process lasted significantly longer. Unlike most democratic transitions, led by either the elite or the people, Chile's democratic transition process is known as an intermediate transition – a transition involving both the regime and the civil society. Throughout the transition, though the regime increased repressive violence, it simultaneously supported liberalization – progressively strengthening democratic institutions and gradually weakening those of the military.

Three factors contributed to the rise of democracy: the economy, the role of the military, and domestic politics. Rapid economic growth (attributed to a low inflation environment), a decline in dictatorship, and the decision of political parties to come together became the main motivation for a broad ideological coalition to be created in an effort to defeat Pinochet and his military rule. Chile was previously a democracy during the Presidential Republic (1925–1973).