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Why was Charles I put on trial in January 1649?

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Painting of the Battle of Naseby shows cavalry and infantry clashing, with soldiers on horseback leading a charge and fallen fighters on the ground amid the chaos of battle. — English Civil Wars *Battle of Naseby*, by an unknown artist. The victory of the Parliamentarian New Model Army, under Sir Thomas Fairfax and Oliver Cromwell, over the Royalist army, commanded by Prince Rupert, at the Battle of Naseby (June 14, 1645) marked the decisive turning point in the English Civil War.

In January 1649, King Charles I was put on trial primarily because he was held responsible for the bloodshed and loss of life during the English Civil Wars, particularly following his role in inciting the second Civil War in 1648.12

After the army forcibly removed moderate members of Parliament in an event known as Pride’s Purge, the remaining group—the Rump Parliament—established a High Court of Justice to prosecute the king. Charles was formally charged with high treason and "other high crimes against the realm of England," specifically being labeled a tyrant, traitor, murderer, and public enemy.123

The trial was driven by the "law of necessity," as the army and the Rump Parliament believed that Charles could not be trusted to compromise and that his continued actions threatened the nation. Throughout the proceedings, Charles refused to recognize the court's legitimacy, arguing that no superior jurisdiction on earth had the authority to try a king.23