When was the last time korea was united?
No context provided
When was the last time korea was united as measured by the time that the PRK was outlawed in the South?
December 12, 1945
No context provided
When was the last time korea was united as measured by the time that the committees were co-opted in the North?
February 1946
Korean reunification
https://en.wikipedia.org/wiki/Korean%20reunification
Korean reunification (Korean: 남북통일; Hanja: 南北統一) refers to the potential reunification of North Korea and South Korea into a single Korean sovereign state. 
Korean reunification
In 2019, South Korean president Moon Jae-in proposed reunification of the two divided states in the Korean peninsula by 2045.[6]
Korean reunification
Korean reunification refers to the potential reunification of North Korea and South Korea into a single Korean sovereign state. The last time Korea was united, as measured by the time that the PRK was outlawed in the South, was December 12, 1945. When measured by the time that the committees were co-opted in the North, the last time Korea was united was February 1946. In 2019, South Korean president Moon Jae-in proposed reunification of the two divided states in the Korean peninsula by 2045.