By 1377 Henry had become the earl of Derby, and in 1380 he married Mary de Bohun, coheiress of the earl of Hereford. In 1387 he joined the opposition to King Richard II led by his uncle, Thomas of Woodstock, duke of Gloucester, and became one of the five "lords appellant" who ruled England in 1388–89. In the early 1390s he served in Lithuania with the Teutonic Knights and went on pilgrimage to Jerusalem.
He supported the king when Richard took his revenge on three of the "lords appellant," including Gloucester, and was made duke of Hereford in 1397. However, in 1398 after a quarrel with Thomas Mowbray, 1st duke of Norfolk, whose confidence he betrayed to Richard, Hereford was banished for 10 years by the king. When John of Gaunt died in 1399, Richard confiscated the vast Lancastrian estates, which were Hereford's inheritance.
The irate duke, taking advantage of Richard's absence in Ireland and the widespread dissatisfaction with Richard's rule, landed in England in July, 1399. He gained ample support, and Richard, who surrendered to him in August, was forced to abdicate. Henry's claim to the throne was confirmed by Parliament in September. He thus, by revolution and election, founded the Lancastrian dynasty.
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