При каком древнерусском правителе Русь вступила в борьбу с другим славянским государством – Польшей?

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Ukraine is a sovereign state. It has its own territory, higher and local bodies of state power, government, national emblem, state flag, and anthem. 
The population of Ukraine is about 52 million people. There are 24 administrative regions there. Many countries have common boundaries with Ukraine and maintain economic relations with it. Ukraine pursues peaceful and neutral policy. It establishes new relations with all countries throughout the world. It sets direct contacts with them signing agreements and treaties. It is one of the founding members of the United Nations Organization and participates in the work of many international organizations. Ukraine is a member of the International Monetary Fund, International Bank of Reconstruction and Development, International Finance Corporation, the European Bank of Reconstruction and Development, the North Atlantic Council of Cooperation, and others. 
The main river in Ukraine is the Dnipro which divides it into Right-bank and Left-bank territories. Sea transport plays an important part in Ukraine’s economy. The ports of the country ensure trade contacts with over 80 countries.