When the United States of America had once acquired the extensive territory known at the beginning of the century as Louisiana there was no effective bar to their extension westward until they came to the shore of the Pacific. There were hostile Indians, and deserts difficult to traverse in the slow-going wagons, but the westward progress of the pioneers went on with no serious sets-back and at a pace which was very wonderful considering the conditions. When the railway era came--we may date its beginning approximately at 1830--the progress was much accelerated. The population of the States grew very fast, both by the increase of the old settlers and by immigration, especially from Ireland. Ireland never had been happy in her Union with England, and her people were discontented and very ready to try their fortunes under the American flag. Just before the middle of the century the potato, on which the Irish people chiefly live, had failed almost entirely, and there had been cruel famine and distress, which further encouraged them to emigrate. Thus America grew great. We have seen that as early as 1823 she had put forth that announcement known as the Monroe Doctrine, which proclaimed that she deemed the whole of the vast South American Continent, as well as the whole of the North which lay {209} south of the Canadian border, to be her concern, and hers alone. She would allow no European nation to interfere there. [Sidenote: The South American states] That did not imply that she herself would seek to upset arrangements already made. What did happen in that South American section was that it was divided into a number of States, which never became united, as did the States of the North. Most of them, very soon after their settlement, had become self-governing, their mother countries in Europe being too war-weary to make very serious efforts to retain them. Spanish was the language of the majority, but in the State which had by far the largest territory of all, that of Brazil, which had rather unexpectedly fallen to the share of Portugal under the dispensation sanctioned by the famous Bull of Pope Alexander, the common language was Portuguese. The population in all of them varied from pure European to pure Indian, with every possible degree of mixture between. Side by side, on the north-east shoulder of the Continent, were, and are, the three Guianas, the British, French, and Dutch. But whereas these three still are European possessions, over all the rest of the Continent the settlers soon threw off all allegiance to their mother lands, as also did Mexico, once known as New Spain, at the southern end of the Northern Continent.