1) What is the definition of terrorism? Would one nation reacting against another be terrorism?
Of course not, the definition may not be standardized by the UN, but the delegate must turn to logic in situations such as these. When one nation turns against another, this is called War. Follows the Cambridge definition of the word;war noun
/wɔːr//wɔːr/ n [C or U]
armed fighting between two or more countries or groups, or a particular example of this
2) A smart nation does not respond, it prevents, like Russia implimenting ABMs
Russia's success in doing this is inspiring. It seems that there is a small difference in our definition of prevention. If by 'prevention', the delegate of Russia means systematically hunting down and killing terrorists as Russia has done for almost 20 years now with the so called 'Chechen' terrorists, then yes, the UK does agree. Quick historical reminder, following the events in Beslan and in the Moscow Theatre, your country 'prevented' (assuming my initial interpretation of your meaning of the word is correct) any future attacks by targeting and killing the heads of the terrorist cells responsible for the attacks. And since when ABM systems will stop terrorists? Terrorists do not have ICBMs, countries do. Countries as your protèges, the DPRK and Iran.
Of course, the other interpretation of the term 'prevent' refers to fortifying security so as to minimize casualties. But we know, especially after our experiences with the IRA and the 'Chechen' terrorists, that they will not stop until they get what they want. There are no effective preventive' measures we could implement so as to effectiveley reduce the risk of future terrorist attacks to zero. We know this, you know this. Unless we go after them, they will continue carrying out their attacks, and even if so much as ONE civilian dies as a result of terrorist attacks, we will have failed. The UK for one, prefers 1000 dead terrorists than one dead civilian. Historically, the Russian Federation has also agreed with this, and the UK is sure that Russia, with its vanguard way of dealing with terrorists, stands by that belief today.