The differences in standard voltage across the United States (110V) & India (220V) can be attributed to historical & practical considerations.
During the late nineteenth and early twentieth century, as commercial electricity distribution emerged, different countries established varying standards that were influenced by technology improvements, economic considerations, & safety regulations. Higher voltages allow for more efficient transmission over long distances with less loss, making them ideal for highly populated areas such as India.
Additionally, safety requirements and grid design influence voltage norms. While efforts for worldwide harmonization are ongoing, appliance compatibility & historical infrastructure continue to influence voltage norms in various nations.