In OTL, many things happened. In this ATL, two different things occurred. The first and most important is that they advanced rapidly, making it to roughly 1600 technology by 1480. The second change is that a massive crusade was organized in 1399, to combat the horde of Muslims which surrounded Europe. By 1498, there had been roughly five wars separated by brief periods of peace.
Following the Treaty of Constantinople in 1498, everything east of the Elbe and south of Vienna was occupied by the Muslim Hordes. The continent had been brought to its knees, with three generations of men, young and old, were dead, and buried beneath the fields of posies, with the posies watered by Europa's tears.