As for the US, the headline does mention Greenland and the article includes

Denmark’s military changes also come in the wake of growing political tensions with the U.S. over control of Greenland, a Danish territory.

And “why Russia tensions?” Probably because Russia is currently waging a war of territorial expansion and several NATO members in the Nordics and Baltics could be next.

Regarding potential conflict with Russia, Denmark’s Minister of Defense Troels Lund Poulsen said in February, "Within two years, Russia could pose a credible threat to one or several NATO-countries if NATO does not build up its own military power in the same rate as Russia.