Final answer:
The main impact of the Ottoman Empire's expansion throughout Southwest Asia was becoming the largest Muslim Empire, notable for its military power, control of trade, and societal diversity. The option (C) is correct.
Step-by-step explanation:
The major impact of the Ottoman Empire spreading throughout Southwest Asia was that it became the largest Muslim Empire of its time. The empire's expansion, which began under Osman I in the 13th century, brought with it a surge of growth in wealth, power, and cultural diversity.
The Ottomans were noted for their military advancements, economic control over trade routes, and the integration of diverse populations under a single politico-religious system. The millet system allowed different religions to regulate their own communities, leading to a remarkable level of societal stability. Istanbul, under Ottoman rule, became a major hub connecting Europe with Asia and Africa. The empire's significance in history is underscored by its long tenure and the legacy it left on the regions it ruled. Therefore, option (C) is correct.