Two theories would be that children learn through watching (like watching parents interact, react, and communicate with others), and by doing (hands-on activities)
6th amendment, which guarantees a lawyer
A letter written during the time a historical event occurred is a useful primary source document.
Primary source documents are the most original way to understand Historical events.
If it was the letter written for discussing analysing the same historical event after the occurrence of the event, it would have been considered as a secondary source.
The leader of the Soviet Union Nikita Khrushchev wanted to put nuclear missiles in Cuba. The reason for this is because Khrushchev wanted to threaten the United States. Since he wanted to threaten the United States, he decided that Cuba, which had recently had a revolution to become communist, was the perfect asset to use in threatening in the US.