Russia used an antisatellite weapon against an old Russian satellite. Such tests create space debris, which we don't have a way to clean up. That is a grave, persistent, accumulating problem.

The ultimate danger of space debris is that a chain reaction of collisions could make so much debris that it would destroy all satellites, and we could never put up satellites (or spacecraft) again. An accelerated version of this was shown in the movie Gravity. I think that was unrealistically fast, but no one would dare build and launch a spaceship if its collisional half life were as little as ten years. Everything human would be excluded from space, except for the hypersonic nuclear missiles that China and the US are testing. (They don't need to stay in space for very long.)

The US tested an ASAT missile and was rebuked for wantonly creating space debris.

Every so often I see a proposed system for cleaning up space debris, I don't think any of them would scale to the amount of debris present in Earth orbit in recent years.