The correct answer is "accepting converts to Islam".
They were the first that started creating a universal Islam identity instead of just catering to the needs of Arabs. Many non-arabic persons started speaking Arabic languages and the spread of the Arabian culture had many people convert to Islam.
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An enormously influential biological exchange occurred when Europeans landed in the Americas, to the benefit and detriment of Europeans and Natives. Old World—New World plant and animal exchange resulted in sugar and bananas crossing the Atlantic while pigs, sheep, and cattle arrived in the Americas. The transfer of European diseases had catastrophic repercussions: influenza, typhus, measles, and smallpox devastated the Native American population. The Biological Exchange (also called the Columbian Exchange or Grand Exchange) is one of the most significant biogeological events of world history, affecting almost every society on earth and historians have only recently begun to question the event and the way it has been traditionally interpreted. In the traditional interpretation of the Biological Exchange, Indians lived in harmony with their environment in a pristine world and both the Natives and the environment were suddenly devastated following the arrival of Europeans. Biological exchanges of plants and animals enabled a better and longer life for Europeans, who took food items like potatoes and corn back to the old world were suddenly able to grow food to support their large population while reducing the population overgrowth by transporting humans to the new world.
