The British were involved in this nasty episode, though only on the margins. All wars are horribly wasting, but this one could be taken as the best example. It was about religion, which hardly comes as a surprise. It is amazing that most human conflict since the death of Christ has come about because of differences of opinion and dogma, when Christ taught that all men should love each other. How humans have reacted during the centuries after His death is hardly His fault.
Thirty Years of almost constant war in Europe arose at first because of Protestant refusal to see a Catholic king on the throne of Bohemia. This was contentious enough but the conflict spread into a confusing religious-political struggle achieving nothing except bloodshed on a grand scale, destruction of towns and property, the fighting followed as usual by plague and famine in Germany herself and her neighbours.
It began in 1618 with a Protestant-Bohemian revolt against the future Emperor, Ferdinand II; it also engendered the Dutch Revolts after 1621 as well as the Franco-Habsburg confrontation in the years after 1635.
The Emperor appeared unscathed by the Bohemian revolt, and helped by Spanish and Bavarians conquered the Palatinate of Frederick V (who had married Elizabeth, a daughter of James I of England). Sadly, his German ambitions plus his Spanish alliance (Roman Catholic) frightened Europe’s many Protestant nations, as well as France. In 1625 Christian IV of Denmark renewed the war against what he called ‘the Catholic Imperialists’. He was the leader of an entirely anti-Habsburg coalition organised by the Dutch.
Denmark did not do at all well out of the growing conflict and after a series of defeats withdrew from involvement at the Treaty of Lübeck (1629). The Emperor then reached the height of his considerable powers. But then Sweden joined in the bloody squabble, in the form of Gustavus Adolphus, so Europe now had France, Germany, Bohemia, Denmark and Sweden involved in an interminable war.
In 1632 the Swedish king was actually killed fighting at the Battle of Lützen and the world looked on in horror as the Swedish Government under Oxenstierna financed and organised the Heilbronn League of German Protestants (1633), but this coalition broke up after a heavy defeat (with the usual loss of thousands of lives) at Nördlingen in 1634.
In 1635 the civil war within Germany was ended by the Treaty of Prague, but people had hardly got their breath back when France, allied with Sweden and the United Provinces, attacked the Habsburgs. Most of the most serious issues were resolved (after five years of negotiations) at the Treaty of Westphalia (1648) but the war between France and Spain was to drag on until the Treaty of the Pyrenees in 1659, so really this appalling chaos could be described as the Forty-One years War.