International Treaties make the most sense as a the major limiting factor
Your question disallows any economic reasons not to use them, Therefore
The big reason you cant use technology to defend against nukes in our world
Assuming that both sides own or have access to the ICBMS capable of long range destructions. and access to large h-bombs. Whilst not yet suggested by anyone else here intercepting hydrogen bombs is impossible. Whilst long range bombers and ICBM's can be intercepted by rockets and missiles. Dropping a large bomb at the bottom of the north sea on a timer would create a tsunamis capable of drowning everyone in Vienna Austria. ICBMS were meant to quickly take out command infrastructure in the hope it would cripple more devastating responses. No missiles shield or submarine screen would prevent a Russian submarine for example from drowning the west coast of north-America by dropping a bomb past Hawaii The pacific is just too big for that. 527
Therefore any technology solution to defend a nation from hydrogen bombs is very costly and unlikely. Unless said nation lives far away from any coast and I mean far far away like for example in the Ural mountains.
Treaties are therefore the only logical reason ###
For example a treaty could ban the use of any large bomb on a mostly civilian target. Even though in WW2 we bombed cities and factories regardless of status. nuclear bombs could be more severely regulated than other munitions. Maybe there is a committee of neutral nations that have to pre-approve the use of nuclear bombs' to make sure the wind doesn't blow radiation into other nations not related to the wars. Or there are designated warzones were certain types of bombs of limited strengths are allowed.
Another exception cloud be international waters away from coasts lines. This could mean that certain size war-heads could be pre-approved by treaty for use in international waters as long as its far away from a port city and does not create a tsunami too large.
There are myths out there that treaties like the Genève convention banned the use of triangular knife's/Bayonet's in warfare because it was harder to treat. Even though that fact isn't true its shows the perceptions that warfare can be limited and regulated affair. 347