I don't think you are worrying unnecessarily as I think there are signs that we could be leading to a major war. There have been other times though that a nuclear war could have broken out but didn't (To give one example, I saw a documentary about a Russian Submarine soldier who was given an order to strike with a nuclear missile on a US target, as the Russians thought they were about to be attacked. He refused to follow the order. It turns out the Russians were misinterpreting signals from a US Plane).
So it is possible we will go many years without a war in Europe (but there are wars constantly going on across the world), but I think major economic meltdowns, which might be almost as bad as war, are inevitable (and economic meltdowns often bring war/conflicts). Our monetary system is frightening, it sounds like a giant Pyramid Scheme only maybe a bit worse. Money as Debt is a scary documentary
Countries are much more intertwined economically than they used to be, a crisis in one country can affect another miles away very quickly. There are political, military and economic alliances that could drag countries into a major war quite quickly. This is what happened with WW1, which most people didn't realise at the time would be a major, world-map changing, war until it was over.
The speed with which countries ran to war then was also partially because no country wanted to be beaten by the other, so they basically tried to get in quickly and beat the other country before they got beaten (There is a saying "The First World War was started by train timetables" and there is some truth to this).
Nuclear weapons could give more urgency to these choices, and ironically a nuclear war, or major war, could break out in a bid to avoid getting obliterated oneself. I would love to think the world leaders are not crazy enough to start a nuclear war, but as they almost started them before, and there are some crazy leaders out there, I don't think we can depend on them to be cool-headed. There are people in the US (e.g. Christian Zionists, who are well connected politically) who look forward to the end of the world. Palin talked with enthusiasm about the coming "rapture" at the end of the world. There are plenty of crazy, or self-deluded, leaders elsewhere as well. Putin is a thug who is power hungry (and creating rival military and economic alliances to the US).
I think the US is the most dangerous power and the most likely to tip us into war, but really any of the big countries could do it. The US is an empire in decline. The wealthy leaders are grabbing on for power/resources where they can in order to maintain their position. This is an interesting perspective on the potential road to WW3
But there is no point in being crippled by worry either as it won't help anyone. You could join an anti-war group, or one that resists neo-liberalism would be good (so anything resisting privatisation, or resisting cutting back on the welfare state, or resisting policies that deregulate the financial sector). Even just getting more informed is good.