Which fundamental force was unified with electricity and magnetism in the 19th century?

In the 19th century, James Clerk Maxwell showed that electricity, magnetism, and light are all related through a single theory: electromagnetism. His equations, published in the 1860s, predicted electromagnetic waves traveling at the speed of light. This was a major step toward modern physics because it revealed that visible light is one form of electromagnetic radiation. Later experiments by Heinrich Hertz confirmed electromagnetic waves experimentally. Electromagnetism now explains everything from chemistry to electronics.