Globalization has occurred in various forms throughout history, from ancient civilizations trading goods along routes like the Silk Road, to the modern era of reduced trade barriers and global corporations. While some point to the modern age as the start of globalization, others argue it began as early as the Sumerian and Indus Valley Civilizations exchanging trade links. Key developments that expanded globalization included the Islamic period promoting trade, European colonialism in the 15th-16th centuries, the Industrial Revolution increasing production and exports, and the 20th century establishment of international organizations like the UN and WTO.