British control of the Straits of Melaka, prompted the Sultan of Siak in 1840 to accept the offer of a new treaty to replace the agreement they had made earlier in 1819. This agreement made the Siak Sultanate area smaller and sandwiched between other small kingdoms which were protected by Britain. Likewise, the Dutch made the sultanate a protectorate of the Dutch East Indies government, after forcing the Sultan of Siak to sign an agreement on 1 February 1858. From the agreement, the sultanate lost its sovereignty, then in every appointment of a new sultan, the sultanate must get approval from the Netherlands. Furthermore, under regional supervision, the Dutch established a military post in Bengkalis and banned the Sultan of Siak from making agreements with foreign parties without the approval of the Dutch East Indies government.