There are too many wars. Wars happen when diplomacy fails. When wars end talking has to resume. A victor in war can lose the peace.
Wars are necessary when a bully state seeks to damage or occupy others. Such a rogue state has to be confronted and defeated if talking does not change their mind. Democracies do not usually covet the land and people of another. The great democracies of North America and Europe have no imperial ambitions to conquer territory or use force to take over the government of foreign lands.
The paradox is that if you want peace you do often have to arm for war. The West keeps up its military capability but rightly calls it Defence. NATO is a defensive alliance. Each member pledges to come to the aid of any member who is attacked, though each member state retains control over their individual contribution to any planned NATO action.
The West has fought in many regional and local wars since 1945. Some would say we have intervened too often. Toppling dictators in the Middle East who were a threat to some of their own citizens and to their neighbours was not always a good idea, as establishing a better government with local democratic consent afterwards proved difficult. Many of the conflicts followed from the dreadful attack on the USA called 9/11. The USA understandably wanted to retaliate,but got dragged into a series of wars where the forces on the ground were complex.
The UK needs to have sufficient military strength to offer protection to these islands. It does so through the power of our own independent armed forces and through our membership of NATO which makes allied support likely in the event of a military threat. The UK also needs to be able to participate in NATO and UN approved actions with an expeditionary capability to project power anywhere in the world. Cutting defence spending or undermining the independent deterrent would reduce our capacity to see off a potential enemy, and could reduce our ability to help our allies and make our necessary contributions as a member of the UN Security Council. The UK is right to retain control over the use of our own armed forces, with a veto over whether to join or to decline any EU military activity. The UK also needs to ensure it has sufficient control over the technology and capability to produce weapons and fighting machines in the UK.