 Under his leadership and in cooperation with the Land's Advocate of Holland Johan van Oldenbarnevelt, the Dutch States Army achieved many victories and drove the Spaniards out of the north and east of the Republic.Maurice set out to revive and revise the classical doctrines of Vegetius and pioneered the new European forms of armament and drill.During the Twelve Years' Truce, a religious dispute broke out in the Republic, and a conflict erupted between Maurice and Van Oldenbarnevelt, which ended with the latter's decapitation.