The DC Animated Universe timeline that I devised consists of the history of Earth-16, where the series Young Justice takes place in.
However, please note that this timeline is unofficial. That is, this timeline is created from my own personal observations and research. In order to make sure that this timeline maintains it consistency and validity, I had to incorporate many assumptions and constraints.
An assumption is easy enough to understand. I take a vague statement and add my own thoughts on what that means. For example, producer, Greg Weisman states that Robin is 13 years old and has been active for 4 years. I assume that Robin was 9 years old when he started out.
A constraint is something, in this case fact, that is binding and can not be modified. For example, in "Independence Day", it is shown onscreen five times that the date is July 4th.
With that said, here is the The Earth-16 Timeline.