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Why did Henry III ally with Henry of Navarre in 1589?

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Henry IV Henry IV, undated copperplate engraving.

In 1589, King Henry III allied with his cousin, Henry of Navarre, primarily as a matter of political survival against the Holy League.12

Following the assassination of the duc de Guise by royal order in December 1588, the Holy League—led by the new head of the house, the duc de Mayenne—declared open war on the king. Having lost control of Paris and facing a powerful Catholic faction that sought to depose him, Henry III found himself increasingly isolated and powerless.132

By the spring of 1589, the king had little choice but to seek protection and military support from Henry of Navarre, the Huguenot leader and heir presumptive to the throne. This alliance allowed the two leaders to combine their forces to hem in the Leaguers and lay siege to Paris, the stronghold of the League's opposition.142