The two mountain ranges generally considered to form the distinction between Europe and Asia are the Urals and the Caucasus. With rivers it's trickier, since there have at times been various interpretations of the distinction between Europe and Asia. I use the 'neutral' word 'distinction' since 'border' overstates the preciseness of the changeover.
Eastern Europe is bordered by Western Europe and Asia as well as the Mediterranean and Black Seas.
The closest to a monarchy from eastern Europe is Liechenstein. It is on the border of eastern and western Europe. Prince Alois has been ruler of the country since 1989.
Eastern Europe is the Eastern portion of the continent of Europe. The countries that border Western Europe are Poland, Slovakia, Hungary, Russia, and Slovenia. Then it includes the in between parts of these countries and Asia.
The Mississippi River
Western Europe. Eastern Europe is used to denote those countries that fell under the influence, or were part of the Soviet Union after the second world war. Finland managed to keep its independence, and is thus considered part of western Europe. Though i would like to note that the boundaries of eastern and western Europe have started to fade. Finland is in Western Europe, it is a border country of Eastern and Western.
Nebraska has a south-western border with Colorado and eastern border with Iowa.
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The Mississippi River forms Tennessee's western border.
It is about 70 miles from the eastern to western border of New Jersey.
The Ural Mountains mark the eastern border of Europe.
The continent that does not touch the eastern border of Europe is North America.
The term iron curtain was used by Winston Churchill to describe the border between communist western Europe and democratic eastern Europe.