The correct answer is: "the Korean War".
The Korean War was fought between 1950 and 1953. It was considered a proxy war in the major conflict known as Cold War, that confronted the Eastern bloc of communist countries leaded by the URSS and the Western bloc of capitalist countries headed by the US.
When the Korean War started, the country had splitted in two halves and North Korea attempted to invade South Korea. The communist North was supported by the URSS and China while the South was supported by the US. This is why defense spending experienced an increase.