Balkans Security Cooperation Act This bill requires the Department of Defense, with the concurrence of the Department of State, to report on security cooperation between Western Balkan countries and the United States, Russia, China, and NATO. For the purposes of this bill, the Western Balkan countries are Albania, Bosnia and Herzegovina, Croatia, Kosovo, Montenegro, North Macedonia, Serbia, and Slovenia. The report must include (1) an assessment of how Western Balkan security cooperation with Russia and China affect the security interests of the United States and NATO; (2) an assessment of the Russian Humanitarian Center in Nis, Serbia, and any influence or coordination it may have with Russian intelligence agencies; and (3) a determination by the State Department on whether any Western Balkan country has conducted a significant transaction with a person that is part of Russia's defense or intelligence sectors.