For it can literally can be used to justify imperialism.

Julius Caesar invades Gaul with his legions. The Gauls are reactionary, why did they not immediately surrender to superior Roman culture? They are backward savages that live in huts, they should forsake their culture and traditions before the majesty of Rome. The native Americans are reactionary for resisting, why did they... you get the point.

Oh look, there's some random 'backward' country that does not share our values, let's invade them and cause a refugee crisis. Hooray. More money for the military industrial complex from human suffering. Let's call them reactionary if they don't want to accept our world view upon them.

Gondor is reactionary to Mordor. Why did Gondor not bow before Mordor's might and accept Sauron as the true lord of Middle-earth? Why did they try hopelessly to stop Mordor's endless legions?

7777039 Ukraine is so reactionary because they're defending themselves. Who doesn't want to be forcefully invaded?

7777039
That's why summaries are useless and must be discarded as lies. They will never give you the whole picture.
Full context and history must never be allowed to be hidden from the public.

The term reactionary is usually a term to refer to the extreme right, though it is sometimes used as an insult rather than objective assessment. It can sometimes be used to demonstrate a more general overreaction though.

I first heard the term used in Victoria 2(a game) and that likely gives me a different context to it than most other people. Reactionary SHOULD NOT be an insult, and it has a place and role as a descriptor. I used to describe myself as such in my teens.(being a monarchist with little to no faith in democratic systems)

It really makes no sense to use it to describe anything in context of outside forces though, a reactionary just thinks that progress has gone down a self destructive road.

That said, I don't really use the term anymore, because its too relative, are you reactionary to democracy, reactionary to the wokeist movement, or reactionary to the counter woke movement? It has no defined starting place, you can bounce it indefinitely. It very much starts smelling of the "there is no left in the US, only far right and further right" argument people unironically make.)

Realistically it be best if people just defined themselves by what end goal they are actually trying to accomplish and what they want from their government, but I think that ultimately people are too apathetic to have a real view on things, they don't want any one outcome, they just want to be part of the wining side.