it's a reference to two houses of England fighting over the throne. Here's what I gleaned online:

The name Wars of the Roses is based on the badges used by the two sides, the red rose for the Lancastrians and the white rose for the Yorkists. Major causes of the conflict include: 1) both houses were direct descendents of king Edward III; 2) the ruling Lancastrian king, Henry VI, surrounded himself with unpopular nobles; 3) the civil unrest of much of the population; 4) the availability of many powerful lords with their own private armies; and 5) the untimely episodes of mental illness by king Henry VI.

The yorkies would have been telling the lancastrians to fall in battle so their hero and leader would be king and the bloody war would be over. Go down means "get out of here." or "die." Imagine a lookout on a hill watching the lancastrians trying to organize themselves for a dawn attack. Under his breath, he's saying, "Go down." Don't come up the hill. Get out of my sight.