The exact size, of course, depends on the playing time (in minutes and seconds), on how good the original compresses and the compression quality. 1 Mb a minute is a good approximation, in practice. I wouldn't trust 2 Gb to hold 1000 average downloaded songs. Just go for 4.
The causes of the Vietnam War were derived from the symptoms, components and consequences of the Cold War. The causes of the Vietnam War revolve around the simple belief held by America that communism was threatening to expand all over south-east Asia.
The long-term causes of the Cold War are clear. Western democracies had always been hostile to the idea of a communist state. The United States had refused recognition to the USSR for 16 years after the Bolshevik takeover. Domestic fears of communism erupted in a Red Scare in America in the early Twenties.