Final answer:
The Oder River rises in Moravia, which is part of the Czech Republic, and then flows into Poland, emptying into the Baltic Sea.
Step-by-step explanation:
The country where the Oder River originates is the Czech Republic, specifically in the historical region of Moravia before flowing northward into Poland and eventually draining into the Baltic Sea.
The Oder River has been significant historically, serving as a natural boundary and playing a role in treaties and geopolitical changes, such as those following World War I. For instance, the establishment of the Polish Corridor as part of the Treaty of Versailles gave Poland access to the sea at the expense of German territory, contributing to tensions leading up to World War II.