Its pretty hard to win wars these if both strong countries are involved. I mean there are so many technological advanced weapons available these days that once simply blow something up from sitting in their house. And its not just one country that has sophisticated weapons. Most of the countries seem to have these kinds of deadly weapons.
No it is not impossible to win a modern war, but in modern wars, most nations do not try to hurt and weaken the enemy until a complete surrender. In modern warns, most of the nations instigating the conflict have other objectives besides complete surrender. That is, they want to weaken a terrorist cell or some other limited objective. Unconditional surrender is still an option in a modern war, but most nations do not choose that to be their goal.