

pH doesn’t necessarily tell the right story if you are concerned about acidity for your teeth, GI tract, or taste. Something like distilled water will turn acidic with a pH of 5.8 due to co2 absorption. There’s barely any “acid” there, though, it just doesn’t have any buffering capability compared to water with some dissolved solids in it (like tap water). What really matters is what they call “titratable acidity”.
https://link.springer.com/chapter/10.1007/978-3-319-45776-5_22
Basically an allied country having a base in your country means that any attacker would presumably also have to attack your ally, drawimg them into the conflict. Obviously agreements like NATO article 5 can do that, but people can back out of agreements. Physical presence is more binding than paper.