Which historical factor explains the leading religion in Albania, Kosovo, and Bosnia and Herzegovina (the countries shaded dark orange)?

The leading religion in Albania, Kosovo, and Bosnia and Herzegovina is Islam. This can be explained by the historical influence of the Ottoman Empire in the region, which ruled over these areas for centuries and introduced Islam as the dominant religion. The legacy of Ottoman rule has had a lasting impact on the religious demographics of these countries, with a significant population adhering to Islam to this day.