Nicholson was exposed to French activities on the Mississippi River while governor of Maryland. He warned the Board of Trade in 1695 that the French were working to complete the designs of explorer Robert La Salle to gain control of the river and dominate the Indian relations in the interior, which "may be of fatal consequence" to the English colonies. He reiterated the warning in a 1698 report, and suggested that the Board of Trade issue instructions to all of the governors encouraging the development of trade with Indians across the Appalachian Mountains. "I am afraid", he wrote, "that now please God, there is a peace, the French will be able to doe more dammage to these Countrys, than they were able to doe in the William's War ." These observations were among the earliest anyone made concerning the threat French expansion posed to the English, and some of his suggestions were ultimately adopted as policy. He actively promoted the idea of expansionist trade on the frontier with other colonial governors, including Bellomont of New York, and Blake of South Carolina.