United States and the Soviet Union
In the late 1980s, Eastern European nations took advantage of the relaxation of Soviet control under Mikhail Gorbachev and began to break away from communist rule. On July 31, 1991, the START I treaty cutting back nuclear warheads was signed by Gorbachev and U.S. president George H.W. Bush. In December 1991, the Soviet Union collapsed and the Commonwealth of Independent States was formed. With the ending of Communism, relations between Russia and the United States warmed rapidly.
The aggressive privatization/free market reforms implemented by Russian President Boris Yeltsin during the 1990s were strongly encouraged and supported by the U.S. administrations of George H. W. Bush and Bill Clinton, and by American economists and corporations. However, the reforms, known as "shock therapy", produced a major economic crisis in Russia, resulting in skyrocketing poverty, and the rise of corrupt "oligarchs" who amassed power and tremendous wealth after acquiring control of the former Soviet state industries. Public order and stability deteriorated greatly.
In regard to international affairs, Russia largely stayed on the sidelines during this period but early signs of eventual tensions between the nations were visible during the late 1990s. Although lending tactical support to its historical ally, Serbia, Russia stood aside and did not attempt to block the 1999 Kosovo War in Serbia, even though both Russia and China had strongly condemned it. Yeltsin denounced the Clinton administration's support of Kosovo. Later that year Clinton and Yeltsin clashed over the war in Chechnya and Yeltsin stirred controversy by stating "Yesterday, Clinton permitted himself to put pressure on Russia. It seems he has for a minute, for a second, for half a minute, forgotten that Russia has a full arsenal of nuclear weapons. He has forgotten about that." Clinton dismissed Yeltsin's comments stating: "I didn't think he'd forgotten that America was a great power when he disagreed with what I did in Kosovo."
During the presidencies of Vladimir Putin and George W. Bush, the U.S. and Russia began to have more serious disagreements. Under Putin, Russia became more assertive in international affairs than it had been under his predecessor; under Bush, the U.S. took an increasingly unilateral course in its foreign policy, particularly in the wake of the September 11, 2001 attacks.
In 2002, Bush withdrew the United States from the Anti-Ballistic Missile Treaty in order to move forward with plans for a missile defense system. Putin called the decision a mistake. Russia strongly opposed the 2003 U.S. invasion of Iraq, though without exercising its veto in the United Nations Security Council. Russia has regarded the expansion of NATO into the old Eastern Bloc, and U.S. efforts to gain access to Central Asian oil and natural gas as a potentially hostile encroachment on Russia's sphere of influence.
Officials in the United States expressed concern over their perception of Putin's increasingly authoritarian rule and reversal of democratic reforms, human rights violations in Chechnya, suppression of free speech, alleged murder of political dissidents, attacks on journalists in Russia, and support for highly authoritarian regimes in other former Soviet republics.
Moscow has also been accused of using its natural gas resources to blackmail neighboring countries like Ukraine and Georgia to gain concessions on matters of concern to the Kremlin.
Post–Cold War increase of tensions
 U.S. plan to place missiles in Poland
In March 2007, the U.S. announced plans to build an anti-ballistic missile defense installation in Poland along with a radar station in the Czech Republic. Both nations were former Warsaw Pact members. American officials said that the system was intended to protect the United States and Europe from possible nuclear missile attacks by Iran or North Korea. Russia, however, viewed the new system as a potential threat and, in response, tested a long-range intercontinental ballistic missile, the RS-24, which it claimed could defeat any defense system. Russian president Vladimir Putin warned the U.S. that these new tensions could turn Europe into a "powder keg". On 3 June 2007, Putin warned that if the U.S. builds the missile defense system, Russia would consider targeting missiles at Poland and the Czech Republic.
On 16 October 2007, Vladimir Putin visited Iran to discuss Russia's aid to Iran's nuclear power program and "insisted that the use of force was unacceptable." On 17 October Bush stated "if you're interested in avoiding World War III, it seems like you ought to be interested in preventing them from having the knowledge necessary to make a nuclear weapon," understood as a message to Putin. A week later Putin compared U.S. plans to put up a missile defense system near Russia's border as analogous to when the Soviet Union deployed missiles in Cuba, prompting the Cuban Missile Crisis.
On 14 February 2008, Vladimir Putin again announced that Russia might have to retarget some of its rockets towards the missile defense system, claiming that "If it appears, we will be forced to respond appropriately – we will have to retarget part of our systems against those missiles." He also said that missiles might be redirected towards Ukraine if they went ahead with plans to build NATO bases within their territory, saying that "We will be compelled to aim our missiles at facilities that we consider a threat to our national security, and I am putting this plainly now so that the blame for this is not shifted later,"
On 8 July 2008, Russia announced that if a US anti-missile shield is deployed near the Russian border, they will react militarily. The statement from the Russian foreign ministry said "If a US strategic anti-missile shield starts to be deployed near our borders, we will be forced to react not in a diplomatic fashion but with military-technical means." Later, Russia's ambassador to the United Nations Vitaly Churkin stated that "military-technical means" does not mean military action, but more likely a change in Russia's strategic posture, perhaps by redeploying its own missiles.
On 14 August 2008, the United States and Poland agreed to have 10 two-stage missile interceptors – made by Orbital Sciences Corporation – placed in Poland, as part of a missile shield to defend Europe and the US from a possible missile attack by Iran. In return, the US agreed to move a battery of MIM-104 Patriot missiles to Poland. The missile battery would be staffed – at least temporarily – by US Military personnel. The US also pledged to defend Poland – a NATO member – quicker than NATO would in the event of an attack. Additionally, the Czech Republic recently agreed to allow the placement of a radar-tracking station in their country, despite public opinion polls showing that the majority of Czechs are against the plans and only 18% support it. The radar-tracking station in the Czech Republic would also be part of the missile defense shield. After the agreement was announced, Russian officials said defences on Russia's borders would be increased and that they foresee harm in bilateral relations with the United States
On November 5, 2008, Russian President Dmitry Medvedev in his first annual address to the Federal Assembly of Russia promised to deploy Iskander short-range missilies to Kaliningrad, near the border with American-backed Poland.