If there is a nation with which I have good relations and a military alliance, how do I attack it without suffering some diplomatic penalties for betrayal? Is there some correct way to proceed?

Simple as

I just saw that I can grab it for like 7 bucks (don’t ask where), and now I’m thinking about getting back into Total War. Just wondering if it’s actually worth it now and if it’s not still a buggy mess like it was at launch.

I swear I offered Sparta a trade deal, got offered High, I threw in NAP, still High, I got greedy and tried for military access, went down to Moderate, clicked Trade, got Rejected, I thought okay let's just do Trade+NAP, but even that got rejected, and then so did Trade and NAP individually. Weird. When I look at our diplomacy score I don't see a change in number after the rejected deal....

So I finished a 100 hour grand campaign as unmodded rome on hard/hard and found the initial leg challenging, but once I captured regions with weapon makers or shield makers in them that allowed me to upgrade my armies to level 3 armor/weapons and after i replaced my pre-marian reforms lines with legionary cohorts, my stacks were pretty much invincible. I thought of upping the difficulty to vh/vh for my next campaign, but I am wondering if other (major) factions are by default harder to master than rome a...