You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
In a previous discussion of the war I suggested what if a third side arose from a cadet branch descended from Humphrey, 2nd Earl of Buckingham, who died of the plague, unmarried. What if he did marry, and married a Mortimer, thus giving him issue? Could Buckingham have been a rival to York and Lancaster?
I'd ask if there could be even more sides, but methinks that's not how lineage works.