The Creeks and their allies, the Seminoles, murdered some white settlers, so Monroe sent troops southward to bring them to order. The leader of this force, General Jackson, was such a hard fighter that he soon drove the Indians back into Florida. There, finding the Spaniards had helped them, he burned a few small towns, and killed two English traders, who had also helped the Indians. This might have made trouble, for the United States was just then trying to agree with Great Britain about our frontiers. Still, the work went smoothly on, until part of the northern boundary of the United States (that is, of the Louisiana purchase) was fixed as the 49th parallel of latitude, from the Lake of the Woods to the top of the Rocky Mountains. It was also decided that the Oregon country, then a large tract of wild woodland reaching from these mountains to the Pacific, should be jointly occupied by Americans and British for the next ten years. The following year, the United States made a treaty with Spain, which, for the sum of five millions, sold us East and West Florida (1819). Then our eastern seacoast extended from the St. Croix River, in Maine, all along the Atlantic Ocean and the Gulf of Mexico to the Sabine River. The same treaty decided that the boundary between Mexico and our country should be formed by parts of the Sabine, Red, and Arkansas rivers, and the 42nd parallel to the Pacific Ocean. Spain was very glad to secure five million dollars just then, because the South American colonies had revolted and ceased to supply her with funds. Some of the principal European kings were so afraid that their states would soon follow the example of South America and set up republics too, that they made an agreement to help each other, and even to force the South American republics to submit again to Spain. When Monroe heard of this agreement, or Holy Alliance, he said that, while the United States did not mean to meddle in European quarrels, we should no longer allow any European power to meddle in American affairs. The American continent was for Americans only, and no part of it could ever be seized by any one else. When the Holy Alliance heard of this statement, which is known in our history as the “Monroe Doctrine” (1823), it no longer dared carry out its plans; for Great Britain sided with us against it. The Emperor of Russia, who had been trying to secure more land along the Pacific coast, felt so sure that the Monroe Doctrine would be upheld, that he consented to sign a treaty, whereby he promised never to claim anything on this continent but Alaska, or Russian America, as it was then called.