How to combine multiple lists into one column?

I have multiple columns of dates.

Col 1 Col 2
July 1 June 1
July 2 June 2
July 3 June 3
July 4 June 4

The goal is to combine both lists into a single list (order doesn’t matter)

Goal
July 1
June 1
July 2
June 2
July 3
June 3
July 4
June 4

Is there a formula that can achieve this?
I’ve tried to use the concatenate() function but this just appends text across cells.