If action is not Putin's intention, then the troops are at least being used as a large pressure point, and Russia has previous form on conflict with its near neighbours to give weight to this aggressive posture. The Crimean Peninsula was annexed in 2014, resulting in war in eastern Ukraine involving the separatists. There have been previous Russian interventions in Georgia and Chechnya.
Russia does not want Ukraine to become part of Nato, bringing the Western military alliance to its doorstep.
A direct military standoff between the US and Russia is a non-starter, and while US and European Union sanctions would be the go-to punishment should Moscow launch a ground war, the eastern European power is heavily sanctioned already.
Hence the overt, Western pre-emptive diplomatic pressure and open references to potential military assault.
The most ominous consideration for Moscow lies in US national security adviser Jake Sullivan's comments that the administration is also prepared to send supplies and resources to Kyiv. The US has been increasing weapons shipments to Ukraine.
With the world increasingly divided into regional power blocs, future disputes over territory and influence that could spark major conflicts will be dealt with by groups of countries attempting to suppress the flames before they grow out of control.
China's equivalent of Ukraine to Russia is Taiwan, but there have also been ongoing tensions with neighbours over islands in the South China Sea, and on the land border with India.
The leaderships of Russia and China probably see a weakened, domestically divided US; German Chancellor Angela Merkel leaving the political stage; French President Emmanuel Macron facing re-election next year; and Britain politically and economically self-isolating.
But also apparent are fresh US attempts to ring-fence China with enhanced security ties involving countries such as Australia, India, and Japan, including a long-term project for nuclear-powered submarines for Canberra. The EU and Britain also have an increasing focus on China.
This all raises the question of what constitutes a threat, and the general difficulty of seeing issues from another person or country's point of view.
Ukraine acting as a de facto Nato member would be alarming to Russia's leadership. And former Soviet states have previously joined Nato and the EU. China would consider Aukus and the deepening Quad accord in a negative light.
China and Russia have recently stepped up their military co-operation. Arrayed against that are the other richest countries in the world. And the US has at least 750 bases in 80 countries around the world with troops in places such as Australia, Canada, Britain, Spain, Germany, Italy, Japan, South Korea, Peru, Turkey, Kuwait and Saudi Arabia.
The Biden call with Putin lasted about two hours, with the US leader then briefing the leaders of Ukraine, France, Germany, Italy and Britain.
Earlier this year after a smaller build-up of Russian forces near Ukraine, the US offered Putin a summit in Geneva. Perhaps these new talks will diffuse the immediate tensions even if underlying red lines remain.
