Well, kiddo, a very long time ago, there was a place called Greece, where people spoke a language called Greek and believed in different gods like Zeus and Athena. But, Greece was not its own country like it is today. It was actually under the rule of an empire called the Ottoman Empire, which was based in what is now Turkey.
The Ottoman Empire was pretty big and had control over many other countries including Greece. The people of Greece didn't like being ruled by the Ottomans and wanted to be their own country again. They were also unhappy with many things the Ottomans were doing like taxing them too much and taking away their freedoms like religion and language.
So, in the early 1800s, the Greeks decided to fight for their freedom and independence. This was called The Greek War of Independence. It was not an easy fight. The Ottomans had a lot of power and strength, but the Greeks were determined to win.
Many Greeks who lived in other parts of Europe like Russia, France, and England, supported their fellow Greeks and sent them weapons and money to help them fight. The Greeks also had some powerful heroes and leaders like Ioannis Kapodistrias, who helped organize and lead them in battle.
Finally, after many years of fighting, the Greeks were able to declare their independence on March 25th, 1821. This was a very exciting moment for the Greek people, and they celebrated by creating their own flag and writing a national anthem.
And that, my little friend, is the story of the Greek War of Independence, when the Greeks fought to become their own country and leave the Ottoman Empire.