What is the figurative meaning of "butting up against"?

From here:

In its quest to become a global superpower, China has regularly become entangled in territorial disputes with its neighbors, butting up against international law.

What word would you replace butting up against with to convey the figurative meaning of it?

Some of guesses are: clashing, colliding, opposing, confronting, defying...

Most definitions I found relate to the literal meaning of "two things being physically close to each other".

Thanks!

Solution 1:

I would say it is no stronger than "coming up against". I think "butting up against" comes from joinery: two thick, blunt ends of wood pressing up against each other.

Solution 2:

The intended image is likely to be of butting heads together, like rams or stags fighting.

"China has regularly become entangled in territorial disputes with its neighbors, clashing with international law"...

(PS: I should add that I don't find the originally text particularly inspiring, and have a sneaking suspicion that "butting up against" is used incorrectly, as I would expect to see that particular expression in situations, for example, where one building or feature is adjacent to another, as in these random examples: "the marquee butting up against the building" / "pedestrian esplanade butting up against the building"...)