The 20th century was the era of military coups — mostly in developing countries in Asia, Africa and South America.
The phenomenon was largely associated with the dynamics of the erstwhile Cold War — a conflict fought by proxy between the time’s two superpowers, the United States and the Soviet Union.
Military coups were prominent instruments used by the superpowers to initiate a rapid regime change in countries where a government was perceived to have become a threat to the regional, political and economic interests of the major powers.
Ideology too played a role, but it was only tributary compared to interests which were related more to the realpolitik of the Cold War.
Both the superpowers used their intelligence agencies to infiltrate the politics and militaries of various regimes; they funded and helped plan military coups and then the regimes which came to power through these coups.
The US was most successful in this respect. It backed and funded a number of military coups across Asia, Africa and South America. It then sustained rigid military dictatorships because they were seen as barriers against leftist revolutions, which (as these did in Cuba, Angola and Nicaragua), had the tendency to largely tilt towards the ‘Soviet camp.’
Some of the most brutal coups backed by the US (in South America) took place in Guatemala, Chile, Argentina, Brazil and El Salvador. All were against regimes perceived by the US to have been leftist and allegedly ‘working to establish Soviet influence in South America.’