Why Did Fidel Castro Endorse Salvador Allende?

Rafael Pedemonte, "The Meeting of Revolutionary Roads: Chilean-Cuban Interactions, 1959–1970," Hispanic American Historical Review (2019) 99 (2): 275-302.

Abstract:

Fidel Castro's endorsement of Salvador Allende's revolutionary program in August 1970 was determined by global transformations and changing priorities within both Chile and Cuba. Since 1968, favorable prospects for the Left encouraged Havana to abandon its radicalism premised on the inevitability of armed struggle. Prior to 1970 Chile gradually promoted rapprochement with the socialist world and lessened Cuba's hemispheric isolation, imposed by the Organization of American States. It is within this framework that the meeting between Cuba's and Chile's revolutions has to be understood. Allende, knowing that Castro's support would push the radical Left to side with Popular Unity in the 1970 elections, sent a delegation to convince the Cubans that socialism could be achieved by peaceful means. These events and strategic discussions within Chile and Cuba reveal how the history of the Left needs to be placed in a broad context defined by the complex unfolding of domestic, hemispheric, and international transformations shaping Latin America in the 1960s.

It's a look at the local and global contexts that framed the Cuban decision to embrace Salvador Allende's peace road to socialism, which previously Fidel Castro said was impossible ("electoral opium" and all that). For example:

--The USSR was threatening Cuba if it didn't stop promoting revolution in Latin America, so this was a way to smooth things over.
--Fidel Castro was isolated in the region and wanted to expand trade and other ties. Allende's decision to restore diplomatic relations was a critical starting point.
--The Chilean Social Democrats started that process earlier, so Chile was a propitious place for Fidel to acknowledge political change that did not overthrow the existing order.
--Salvador Allende need the endorsement to get the radical left to vote for him.

Fidel and Allende needed each other:

The encounter between the Cuban Revolution and the Chilean road to socialism in 1970 was not just a response to the contemporary conjuncture but also the fruit of a long-term evolution rooted in previous developments and molded by a complex set of factors.

This is also a reminder that even radical movements can exhibit strong pragmatic impulses. I've made the case for some time that even leftist Latin American governments are more pragmatic than typically portrayed.