Thomas was appointed American Minister for his third and last period on December 18, 1898, until he was recalled on May 31, 1905. In a letter to the U.S. Department of State February 2, 1905, Thomas wrote: "A serious crisis for the union of Sweden and Norway seems very imminent." He was commenting on the growing concerns that the Norwegian government was about to renounce the union with Sweden. He added in the letter that he was convinced there wouldn't be a war between the two countries, and personally he hoped the union could be preserved. He continued, "in this conviction of peace, lies the greatest hope for every friend of Scandinavia, that the union between these two noble nations in the high north, must be preserved in one form or another." In March 1905 he reported home that the Norwegian government had resigned and a new one would be formed. He noted the new one would probably be composed of "members of the extreme left, meaning those who wish for an immediate and radical action in regard to the relationship between Sweden and Norway." This "extreme left" was now prime minister Christian Michelsen, who to all Norwegians would become the leading symbol of the movement towards dissolution of the unpopular union. Thomas' last mission as American Minister ended that spring, he was recalled on May 31, making him in effect, the last US ambassador to the united kingdoms of Sweden and Norway. On June 7, 1905, the union of Sweden and Norway ended, and he would be succeeded by Charles H. Graves.