Why is A horse! a horse! my kingdom for a horse iamvbic pentameter?

The phrase "A horse! a horse! my kingdom for a horse!" from Shakespeare's Richard III expresses desperation and the value of a simple need in a moment of crisis. Spoken by King Richard III, it highlights how, despite his power and status, he is willing to trade everything for the means to escape or secure his position. The line's rhythm, in iambic pentameter, enhances its dramatic urgency, emphasizing the stark contrast between his royal authority and his vulnerable predicament.