The Outer Space Treaty should be considered a postponement, not a prevention, of weapons in space. The temptation is far too strong, and many of the growing space-launching powers of the world are too secretive and closed to be expected to follow it.
The most immediate threat is actually the use of weapons against civilian satellite targets. Completely possible - with 1980’s space technology it could be done, and accidental collisions have already happened. Now Elon Musk is launching even more fodder to make the conflagration ramp up even more quickly once the space junk chain-reaction starts.
There was a certain amount of exaggeration in the movie Gravity, but only in its speed. A chain reaction will soon be possible. Space junk will soon become a politically and tactically advantageous tool against western nations and their economies, once a chain-reaction can be started by countries that are already cutting themselves off, like North Korea and Russia. These countries rely less than western countries do on satellites for the normal daily operation of their economies, and they are on a path were they may eliminate or reduce their dependence, too. Starting a chain reaction could soon be to their advantage.
If not attempting to cause widespread chaos in orbit, there are plenty of more direct ways to destroy things in orbit. The velocities are so high and orbits are so full, it’s becoming difficult to prevent collisions. Then there are the deliberate kinds of targeted satellite kills that have now been done by the USA, India, and China.
We go on about cleaning up the junk - the ESA is getting in on the act with their recent satellite debris cleaner robot. But that’s going to take time to become effective, and ironically, will require a lot of additional spacecraft to carry out a worthwhile collection and disposal.
OK - that’s chapter 1 of my diatribe. I have been uneasy about this for a long time (you can tell, can’t you?)
There are other kinds of kinetic weapon that don’t destroy the attacking spacecraft.
The deployment of nuclear radiation against manned spacecraft does not require an explosion, just the depositing of radioactive material near the space station.
Inhabitants of the moon will have an infinite resource of offensive projectiles to use against targets on the Earth.
The hammer of Thor has been mentioned already.
It goes from bad to worse.
I haven’t even begun on the potential competition to colonize the Moon to use it as a strategic asset.
I don’t think the treaties of the past will be effective at stopping militarization - not when Trump and Xinping or people like them are running the world’s major powers.