What kind of legacy did the native americans leave 2000-3000 years ago to civilisation ? The Romans built roads, acquaducts, conquered the known world, invented Roman Law (that underpins most non common law systems even today). The Chinese had similar accomplishments. The Greeks invented Democracy (although Greek democracy was different from modern day democracies), managed to conquer territories up to India , had great philosophers etc...
Maize. It's probably the greatest example of genetic manipulation in history. Started ~ 10,000 years ago to produce the most productive grain on the planet.
Potato. Wild potato were toxic. Domestication bred less toxic ones. Introduction of the potato into northern Europe helped eliminate famines from the failure of wheat crops.
More recently, the ways and ideas of the native american tribes living in and around the colonists certainly influenced the Declaration of Independence, The Constitution of the United States and The Bill of Rights in the USA.