With mounting tensions between the West and Russia, both sides sent more of their military might closer to the Russian border.

Last week, a new NATO European Missile Defense system went online in Romania, angering Russia.

Romania is also where NATO recently built a new European missile defense system-another one is being built in Poland.

As NATO builds up in Eastern Europe where Russia once ruled in influence, Moscow said it must respond.

Russia’s defense minister says those measures include sending more military units to its Western border by the end of the year.

The NATO-Russia relationship soured two years ago after Russia’s annexation of Crimea.

And experts said as long as Moscow holds Crimea and denies support for pro-Russian rebels in Eastern Ukraine-NATO will want a strong footprint in Eastern Europe.

The next NATO summit will take place in Warsaw in July. At that summit we’ll see if NATO decides to further increase its presence in Eastern Europe close to Russia’s border.