In 1652, the mood in the Netherlands changed due to the outbreak of war with England. Mary's son was officially elected as the stadtholder of Zealand and several northern provinces, but Witte de With, the leader of the republic, prevented William III from being elected in Holland; in addition, when concluding a peace treaty, Cromwell insisted on the adoption of the Act of Seclusion, which prohibited Holland from appointing members of the Orange dynasty to the post of stadtholder. Another requirement of Cromwell was the expulsion of all enemies of the Commonwealth from Holland. Mary made an official protest, but it was not taken into account, despite the fact that the country was threatened by civil war; the peace treaty was signed on 27 May 1654.