|"Is this all real? Or has this been happening inside my head?"
The subject of this article is a real-life person, group, company, product, or creative work that has been mentioned "in-universe" in a canon source. The Harry Potter Wiki is written from the perspective that all information presented in canon is true (e.g., Hogwarts really exists), and, as such, details contained in this article may differ from real world facts.
The War of the Roses were a series of bloody dynastic civil wars between supporters of the rival houses of Lancaster and York, for the throne of England. This conflict is called the "War of the Roses" since the symbol of the House of Lancaster was a red rose, and the symbol of the House of York was a white rose. They are generally accepted to have been fought in several spasmodic episodes between 1455 and 1487 ending with the victory of Henry Tudor, who united the two houses through marriage and founded the Tudor dynasty. It is a popular historical theory that the War of the Roses began as a dispute between wizarding neighbours over a Fanged Geranium. 
- J.K. Rowling's Official Site (First mentioned)