I'd be very happy if we could focus a bit more on making awesome shields than more awesome swords. :v
There's a sort of parallel in the Washington Naval Treaty of 1922. Basically countries felt like they had to continually build bigger and bigger and more and more ships just to keep up with competition. The treaty set a limit on how many and how large of capital ships any given country's navy could be, with some thought put into what would be necessary to patrol a country's given waters. Basically, some countries found the arms race detrimental to their economy and the resources being poured into more and larger ships was a bit of a hole that would never really pay back. A ship would be built with given armor and guns, and then someone else would build one with more armor and guns that could pierce the first's armor and so on and so on.
The treaty was put into place because they realized that the size of guns and the thickness of armor was a race that was ultimately useless, as you could always go bigger up until you ran out of resources.
Now... this was 1922 thinking. The treaty was basically thrown out around WW2 and a lot has changed since then. Not only the development of nukes, but also in conventional weapons. The realization being that no matter how much armor you put on something, a weapon that can pierce or otherwise render that armor useless is going to be significantly cheaper and easier to use.
I have no idea what a "shield" against a nuke would look like, excepting the traditional "a hell of a lot of dirt and rock" or enough empty space that getting the nuke to you would be prohibitive (Mars?), but odds are if you can come up with an armor against a nuke, someone will simply come up with a bigger nuke or some way to pierce that armor that nullifies any sort of advantage it might provide.
There's a reason we've done very little development of our nuclear arsenal since the 80s. We have very strict treaties with Russia that limit what both sides can have and those extend to the defenses we're allowed as well. We've managed to squeeze in the development of a few small scale missile defense systems on the excuse that "rogue states" might acquire a missile and nukes... and that has become true at some point, if not earlier with Iran then at the very least with North Korea. But anything that might hinder a "First strike" from a reasonably developed nuclear country like the US, Russia or China, has been thus far off the table. At least openly. (And in my opinion nothing big enough to hinder such a strike would be able to be hidden for this long nor would it really be worth the destabilizing effects.) Even if one were developed, it would likely be rendered obsolete quickly.