The Soviets and now the Russians have always maintained the policy that first use/strike is an option.
The US, France, and UK do the same.
Israel of course won't admit to having nukes, but they do say they would not "introduce nuclear weapons" into a conflict.
Not sure what Pakistan and India's policy is regarding first strike.
Unless something changed recently, China is the only country who has publicly sworn off first strike.
"If you will not fight for right when you can easily win without blood shed; if you will not fight when your victory is sure and not too costly; you may come to the moment when you will have to fight with all the odds against you and only a precarious chance of survival. There may even be a worse case. You may have to fight when there is no hope of victory, because it is better to perish than to live as slaves." - Sir Winston Churchill