PODGORICA, Montenegro (AP) — NATO is seeking to expand for the first time after six years by inviting the tiny Balkan nation of Montenegro to join the alliance. The move on Wednesday angers Russia, which has strong historic, political and cultural influence in Montenegro and is threatening economic and political retaliation. Here's a brief explanation of how global tensions play out in Montenegro, where the people remain deeply split over whether to join the Western military alliance that bombed the country in 1999.

THE BLACK MOUNTAIN ON THE SEA

Montenegro — which means "Black Mountain" — is a small country in southeast Europe. It is a land of stunning natural beauty, squeezed between the Adriatic Sea and towering mountains, laced with green valleys and rushing rivers. The land area is nearly 14,000 square kilometers (5,300 square miles). Just over 600,000 people live in Montenegro, mostly in the capital Podgorica and along the coast. The economy is weak, relying largely on tourism.

A MOSTLY CHRISTIAN NATION WITH A COMPLEX HISTORY

About 70 percent Montenegrins are Orthodox Christians, which partly explains strong links to Russia, also a predominantly Orthodox Christian country. Until recent history, Montenegro had been a faithful ally of Russia in the Balkans, so much so that it is said to have declared a war on Japan in 1904 just to support Russia in its clash with Japan. Montenegro was also a rare country in the region to have retained a level of autonomy during centuries-long Turkish Ottoman rule.

A DIVORCE WITH SERBIA, AND AN ODD RELATIONSHIP WITH RUSSIA

Montenegro was part of the former Yugoslavia and a union with Serbia in the 20th century. As a Serbian ally, Montenegro was bombed in 1999 by NATO which launched air strike to stop a crackdown against Kosovo Albanian separatists. But, after splitting with Serbia in 2006 in a referendum, Montenegro took a strong turn toward Euro-Atlantic integration, despite Russia's bid to retain political and economic influence. Russian companies have invested millions in Montenegro, which has also become a favorite tourism destination, and Russians have been buying property along the Adriatic sea. There is a pure Russian village on the coast and Russian-language schools were opened for their children.

HOW A TINY NATION IS DIMINISHING THE INFLUENCE OF A HUGE ONE

Montenegro has a small army of just some 2,000 soldiers, but it is strategically located on the Adriatic sea, between NATO members Croatia and Albania, having deep-water navy bases that could be used for big navy ships and submarines. Bringing in Montenegro to the NATO sphere further diminishes Russia's influence in southeast Europe, and blocks it from the so-called "warm seas" in Europe. The Russians are not so much worried about the strategic military loss, but more about their diminishing political influence on the region.

DEMANDS FOR A VOTE, FEAR OF MORE VIOLENT PROTESTS

Montenegrins are almost equally divided over joining NATO. Pro-Russian opposition parties are already demanding a referendum before the entry is formalized next year — mirroring demands by Russian officials. This could lead to tensions after recent anti-NATO protests in the capital Podgorica which have turned violent. Still, pro-Western Prime Minister Milo Djukanovic insists Montenegro's invitation is good news for the country and regional stability. Montenegrin analysts believe Russia will try to finance the Montenegrin opposition ahead of the next general election scheduled for the next year, to try to unseat Djukanovic's government before Montenegro formally becomes a NATO member. The latest opinion poll conducted by the local Damar agency said that 47 percent of Montenegrins are in favor of the NATO bid, some 39 percent are against while 14 percent are undecided. The poll has a two percent margin of error.

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Associated Press writers Jovana Gec and Dusan Stojanovic contributed from Belgrade, Serbia.