Why did Mandela’s point of view on the use of violence against the apartheid government change in the early 1960s?

At first, Mandela and his fellow members of the ANC used nonviolent tactics like strikes and demonstrations to protest apartheid. In 1952, Mandela helped escalate the struggle as a leader of the Defiance Campaign, which encouraged Black participants to actively violate laws.

Explanation:

the berlin blockade was an international crisis that arose from an attempt by the soviet union, in 1948–49, to force the western allied powers (the united states, the united kingdom, and france) to abandon their post-world war ii jurisdictions in west berlin. in march 1948 the allied powers decided to unite their different occupation zones of germany into a single economic unit. in protest, the soviet representative withdrew from the allied control council. coincident with the introduction of a new deutsche mark in west berlin (as throughout west germany), which the soviets regarded as a violation of agreements with the allies, the soviet occupation forces in eastern germany began a blockade of all rail, road, and water communications between berlin and the west. on june 24 the soviets announced that the four-power administration of berlin had ceased and that the allies no longer had any rights there.

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.