The Conquest of Wales by Edward I, sometimes referred to as the Edwardian Conquest of Wales, took place between 1277 and 1283. It resulted in the defeat and annexation of the Principality of Wales, and the other last remaining independent Welsh principalities, by Edward I, King of England. By the 13th century Wales was divided between native Welsh principalities and the territories of the Anglo-Norman Marcher lords. The leading principality was Gwynedd whose princes had gained control of the greater part of the country, making the other remaining Welsh princes their vassals, and had taken the title Prince of Wales. Although English monarchs had made several attempts to seize control of the native Welsh territories, it was not until Edward's war of conquest against Llywelyn ap Gruffudd  of 1277 to 1283 that this was achieved on a lasting basis. In two campaigns, in 1277 and 1282/1283 respectively, Edward first significantly reduced the territory of the Principality of Wales and then completely overran it, as well as the other remaining Welsh principalities. Most of the conquered territory was retained as a royal fief, and these lands subsequently became, by custom, the territorial endowment of the heir to the English throne with the title Prince of Wales. The remainder would be granted to Edward's supporters as new Marcher lordships. Although the territories would not be effectively incorporated into the Kingdom of England until the Laws in Wales Acts 1535-1542, Edward's conquest marked the end of Welsh independence.
Question: How many years did Edward's war of conquest against Llywelyn ap Gruffudd last?
Answer: 6