While Russia’s stated goal in moving into Syria is to fight the Islamic State, NATO’s top commander believes Russia’s new presence includes the first pieces of an intricate layer of defensive systems deployed to hinder U.S. and coalition operations in the region.

“As we see the very capable air defense [systems] beginning to show up in Syria, we’re a little worried about another A2/AD bubble being created in the eastern Mediterranean,” said Breedlove to an audience at the German Marshall Fund Monday.

A2/AD stands for anti-access/area denial. During the early stages of warfare, A2/AD could have been a moat around a castle, or spikes dug into the ground—anything to keep the enemy off a certain swathe of territory. In the 21st century, however, A2/AD is a combination of systems such as surface-to-air missile batteries and anti-ship missiles deployed to prevent forces from entering or traversing a certain area—from land, air or sea. […]