
I’m someone who is very into North American ecology and history and it wasn’t wilderness. North American ecosystems have been artificially managed through controlled burns for thousands of years. You can read early European accounts of the North Carolina piedmont or the New England forests. Large sections of the United States would be more accurately described as parkland than wilderness.
A great many of the early European settlers were also very poor unskilled laborers. Virginia imported massive numbers of indentured servants (including my own ancestors), most were English, but others were from India, Ireland, or Africa. When these servants revolted in Bacon’s rebellion due to demands for land, the planter class shifted towards African chattel slavery to avoid having to provide land to freed former laborers.
thereal._.ruckus mentioned mesa verde as an example of an existing native city and its far from the only one. North America was less urbanized than Mexico but had a number of large settlements, particularly in the southwest and in a region known as the Mississippian culture throughout the Midwest. The largest of these Mississippian settlements like Cahokia and Spiro Mounds were abandoned prior to European arrival, but many were encountered by the Spanish De Soto Expedition in the 1500s
Even early Anglo-Americans expressed fears about foreigners immigrating which never materialized. Benjamin Franklin, for example, was made uncomfortable by German immigration into Pennsylvania. He said they were swarthy and disliked the widespread use of the German language. But it turned out completely fine, as did every other wave of immigrants afterwards. Including the Italians, Irish, poles, and others who immigrated during the industrial age of the late 1800s when the frontier was closed.