As a Brit and in the interest of accuracy, Britain declared war on Germany both in 1914 [0] and 1939 [1] after an ultimatum to Germany expired. So technically 'we' did "start" the WORLD WARs (if we hadn't declared war it is debatable war would have spread to the rest of the world (at least immediately)).

[0] 23:00 August 4th 1914, in response to the invasion of Belgium by Germany.

[1] 11:00 September 3rd 1939, in response to the invasion of Poland by Germany.