the Ohio River. Upon contact with English explorers, the English noted that the lead plates were monuments "of the renewal of [French] possession" of the land. In 1774, Captain James Cook attempted to invalidate Spain's land-claims to Tahiti by removing Spanish marks of possession and then proceeding to set up English marks of possession. When the Spanish learned of this action, they quickly sent an explorer to reestablish their claim to the land. European colonialists developed the legal concept of terra nullius (literally: nobody's land) or vacuum domicilium (empty or vacant house) to validate their lands claims over Indigenous peoples' homelands. This concept formalized the idea that lands which were not being used in a manner that European legal systems approved of were open for European colonization. Historian Henry Reynolds captured this perspective in his statement that "Europeans regarded North America as a vacant land that could be claimed by right of discovery." These new legal concepts developed in order to diminish reliance on papal authority to authorize or justify colonization claims. As the "rules" of colonization became established in legal doctrines agreed upon by between European colonial powers, methods of laying claims to Indigenous lands continued to expand rapidly. As encounters between European colonizers and Indigenous populations in the rest of the world accelerated, so did the introduction of infectious diseases, which sometimes caused local epidemics of extraordinary virulence. For example, smallpox, measles, malaria, yellow fever, and other diseases were unknown in pre-Columbian Americas and Oceania. Settler independence and continuing colonialism Although the establishment of colonies throughout the world by various European powers aimed to expand those powers' wealth and influence, settler populations in some localities became anxious to assert their own autonomy. For example, settler independence movements in thirteen of the British American colonies were successful by 1783, following the American Revolutionary War. This resulted in the establishment of the United States of America as an entity separate from the British Empire. The United States continued and expanded European colonial doctrine through adopting the Doctrine of Discovery as the law of the American federal government in 1823 with the US Supreme Court case Johnson v. M'Intosh. Statements at the Johnson court case illuminated the United States' support for the principles of the discovery doctrine:The United States ... [and] its civilized inhabitants now hold this country. They hold, and assert in themselves, the title by which it was acquired.