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Why did Henry IV invade Italy again in 1090?
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Henry IV
Henry IV, illumination from the manuscript Ekkehardi historia, c. 1113; in possession of Corpus Christi College, Cambridge.
Henry IV invaded Italy in 1090 primarily as a response to a strategic alliance formed against him. In 1089, Pope Urban II arranged the marriage of the 17-year-old Welf V of Bavaria to the 43-year-old countess Matilda of Tuscany.
Because Matilda was a zealous supporter of the church reform movement, this marriage effectively allied Henry’s opponents in both southern Germany and Italy. Faced with this coalition, Henry was compelled to intervene militarily in Italy once more to protect his interests and maintain his authority.1