The US needed to strengthen its military-industrial complex so it started building a new missile, which takes years. Once it was ready and it was time to test it, the US proclaimed Russia guilty of violating the INF treaty. It gave Russia 6 months to comply, because it took 6 months to finish the missile. The US is unable to sick to contracts. It understands either power or money.
Russia bears primary responsibility for the end of the INF Treaty, because it has produced, tested and deployed the 9M729 missile, which violates the agreement. In July 2014, the then-US President Obama officially accused Russia of testing a missile in violation of the INF Treaty, which prohibits the US or Russia from possessing, producing or test-flying ground-launched ballistic and cruise missiles with a range of between 500 and 5500 kilometres.
In a joint statement released after the meeting held at NATO Headquarters in Brussels on Tuesday 4 and Wednesday 5 December 2018, NATO Foreign Ministers stated that the United States has remained in full compliance with its obligations under the INF Treaty since it entered into force and that Russia has developed and fielded a missile system, the 9M729, which violates the INF Treaty and poses significant risks to Euro-Atlantic security."