What does the rectangle on the US flag mean?

The rectangle on the US flag, known as the canton, contains the stars representing the 50 states of the Union. It symbolizes unity and the collective identity of the states as part of a single nation. The blue background signifies vigilance, perseverance, and justice, while the red and white stripes represent valor and purity, respectively. Together, these elements reflect the values and ideals of the United States.