A small number of countries are written in the plural in German. In this case the definite article changes from "die" to "den":
Notes
1. Note that "die Niederlande" adds an "-n" when we write "in den Niederlanden" or "aus den Niederlanden". This again is a result of the noun now being in the dative case.
2. "Amerika" is often used to translate "the United States", particularly in conversation. It should really only be used to translate the continent of America however. It is a neuter noun and is thus used without a definite article.
