I was playing as the UK on the 1936 scenario, no cheats and no mods. A few months in I decide to annex Ireland, which I do. All was still normal for now, but then on September 1936 France declares war on Germany, all of Eastern Europe declares war on the Soviet Union and the allies, Italy declares war on the allies, Republican Spain wins the civil war and joins the allies, Portugal joins the axis, Japan joins noone and declares war on Nat China. Eventually France and I beat the axis into submission and they surrender. Ethiopia gained much Italian lands, South Africa got Angola, Rep. Spain annexes the rest of Portugal with the exception of Asian territories, which were annexed by the UK. France annexed Italy, UK annexed Germany as well as a few Eastern European nations and the USSR annexed the rest, including Poland, who declared war on the axis, comintern and allies at the same time. Japan also got annexed by Nat. China.
WWII ended on April 1938, and the world was at peace. The world powers were the Soviet Union, UK, France, Nat China and arguably Ethiopia (they had a very strong military).
Unfortunately this peace would not last long. On August 1938, the Soviet Union declared war on the UK, as did Nat China. This brought the global allies into the war too. Several other nations declared war on the allies too including large portions of South America and, quite strangely, the US + Mexico. The world was at war for the second time in 5 years, I was thinking to myself "wtf". But regardless, I roflstomped this new axis with my French buddies. I got the US, Brazil, Argentina, the USSR and Nat China. France got Mongolia, Tannu Tova, Cuba, Mexico, Honduras, Haiti, Dominican Republic and the rest of Central + South America. The war ended on February 1940 and France/UK were the only world powers remaining.
Does annexing Ireland REALLY cause such drastic things to happen? My savegame seems to have got corrupted somewhere along the line because now it won't want to work which is a shame, as I would have liked to potentially see France's leaving of the allies and a massive global conflict between the two countries.