How can you explain the similarity of the temples built at different times and in different countries?

Religion. Religion (for example, Christianity) was one among many peoples, separated by huge distances. At the same time, many architects and simply devout people made pilgrimages to holy places and to the iconic cities of their religion (Constantinople, Rome, Jerusalem and others). There they met with the finest works of architectural and religious thought. And so afterwards they tried to make copies in their homeland. By bringing your own style. Therefore, in this way, general forms and styles can be traced in completely different countries.