Complex sentence: Using a plate tectonics definition, Iceland would qualify as a transcontinental country; however, "continents" are not defined by plate tectonics, and geographically, ethnically, historically, and culturally, Iceland is commonly considered to be European and not transcontinental.
Split into simpler sentences: Using a plate tectonics definition, Iceland would qualify as a transcontinental country. Geographically, ethnically, historically, and culturally, Iceland is commonly considered to be European and not transcontinental.