England’s flag is a red cross because it is the Cross of St. George, a medieval symbol that became associated with England and its soldiers, then with English identity more broadly. The simple red-on-white design was used by English crusaders and later adopted as a national emblem.

Why that design

  • The cross is linked to Saint George, England’s patron saint.
  • English forces were using the red cross by the late 12th and 13th centuries.
  • It stood out clearly on battlefields and on ships, which helped it spread as a military and then national symbol.
  • When the later Union Flag was created, England’s red cross was kept as one of its core elements.

In plain English

The flag is not red because of a modern political choice; it is red because that cross became England’s historic emblem centuries ago. Over time, people kept using it, and it stuck.

Today, the red cross is usually called the flag of England or St George’s Cross.

TL;DR

England’s flag is a red cross because it represents St. George and has been used as England’s symbol since medieval times.