Freedom of navigation is a part of international law major powers usually care about, because international trade serves their interests.
Maybe a bunch of small North European countries decide to blockade Russia in the Baltic Sea, and maybe Russia doesn't consider this an act of war, because NATO seems credible enough. Suddenly the Houthi attempt to blockade the Red Sea becomes much more legitimate, and Iran will certainly take note. Maybe Panama goes shopping for allies (since the US is starting to look unpredictable), and maybe China gains the power to decide who gets to use the canal. And maybe Turkey (which is technically a NATO member but not in particularly friendly terms with the West) decides that it is allowed to control access to the Black Sea.
>maybe Turkey (which is technically a NATO member but not in particularly friendly terms with the West) decides that it is allowed to control access to the Black Sea
Interestingly, Turkey is allowed -- by the Montreux Convention -- to close the straits between the Black Sea and the Mediterranean to warships and in fact have been doing so since 2022:
>Turkey has closed off the Bosphorus and Dardanelles straits to warships from any country, whether or not they border the Black Sea, following Russia’s invasion of Ukraine. The strait closures will still allow warships through if they are returning to a home base in the Black Sea, according to reporting from Naval News. This would include Russian ships in the country’s Black Sea Fleet. However, the decision to restrict warships, a power given to Turkey by the Montreux Convention of 1936, will likely limit Russia’s ability to move ships from its other fleets to the Black Sea.
I don't see how things not being considered legitimate by the West currently stops anyone but the West and even that only a little bit, with exception of US that does whatever it pleases all the time.
International politics is not a war of all against all. It's more like a pre-state society governed by informal norms and expectations and personal relationships between the elites.
People like predictable rules. If the big guy says that the seas are open and they are open, you will probably support the rule, because it allows you to focus more on trade and less on protecting your interests by force. But if the seas are open, except for those the big guy doesn't like, then you may start wondering if you'll also end up on that list.
Big guys also try to enforce the rules. If piracy or an unjustified blockade threatens the freedom of navigation, naval powers will try to restore the status quo.
Reciprocity is an important norm in international politics. It makes things a bit like a mix of little kids arguing and common law. The key principle is that if the big guy and his friends area allowed to do X for their reasons, it sets the precedent that you are allowed to do what you consider the equivalent of X for your reasons. Either the big guy follows his own rules, or everyone is allowed to use their own judgment to break the rules. But if a random nobody breaks the rules, it doesn't set the precedent in the same way.
> International politics is not a war of all against all. It's more like a pre-state society governed by informal norms and expectations and personal relationships between the elites.
If someone violates the expectations but is not strong enough to defend his violation then expectations about behaviors of others towards him might be freely violated as well without destroying whole arrangement between conforming parties.
Maybe a bunch of small North European countries decide to blockade Russia in the Baltic Sea, and maybe Russia doesn't consider this an act of war, because NATO seems credible enough. Suddenly the Houthi attempt to blockade the Red Sea becomes much more legitimate, and Iran will certainly take note. Maybe Panama goes shopping for allies (since the US is starting to look unpredictable), and maybe China gains the power to decide who gets to use the canal. And maybe Turkey (which is technically a NATO member but not in particularly friendly terms with the West) decides that it is allowed to control access to the Black Sea.