The chief military exploits of Frederick Henry were the sieges and captures of Grol in 1627, 's-Hertogenbosch in 1629, of Maastricht in 1632, of Breda in 1637, of Sas van Gent in 1644, and of Hulst in 1645. During the greater part of his administration the alliance with France against Spain had been the pivot of Frederick Henry's foreign policy, but in his last years he sacrificed the French alliance for the sake of concluding a separate peace with Spain, by which the United Provinces obtained from that power all the advantages they had been seeking for eighty years.