On 28 Sept 1938, Chamberlain signed the Agreement. Within a year, however, Britain and Germany were at war.
There were many factors which drive Chamberlain to declare war on Germany.

The first was opposition and pressure from within Britain. The Munich agreement caused a lot of anger in Britain. On 3 October, Duff , First Lord of the Admiralty, resigned, and on 27 October, Quentin , a Chamberlain supporter, won a by-election in Oxford, but his opponent is supported by many Conservatives (including Winston ), who claimed: 'A vote for Hogg is a vote for Hitler'. In February 1939, British MPs shouted '' at Chamberlain in Parliament, suggesting that he was a Nazi-lover. All this pressurised Chamberlain to take a firmer stand against Hitler.

Also, events during the year after September 1938 proved that Nazism was a nasty, dangerous and continuing threat. On 8 November - on - the Nazis attacked the German Jews. On 28 February 1939, the Fascist ruler won the Spanish Civil War. On 13 April, (the Fascist ruler of Italy) conquered Albania. And on 22 May, Hitler and Mussolini made an alliance (called the Pact of Steel). Appeasement was being proved to have failed to stop Hitler's aggression.
The most important event was on 15 March 1939, when Hitler invaded . It was the first time Hitler had attacked a people, and it proved to most British people that Hitler would only be stopped by a war. Even Chamberlain said it was a 'shock to '. He promised to defend , which was clearly next on Hitler's list.
Only one thing was stopping Hitler invading Poland, and that was Russia. On 19 May, had suggested an alliance of France, Britain and Russia against Hitler, and on 11 August, British politicians had gone to Moscow for talks with Russia. On 23 August , however, Russia and Germany had signed a treaty, not to go to war with each other, and to attack and Poland between them.
On 26 August Hitler sent armed Nazis to Danzig to stir up trouble, then demanded Danzig and the Polish . On 31 August, Hitler offers to defend the British if Britain let him have Danzig and all former German colonies - it was a mocking offer, and when on 1 September Britain refused, Hitler invaded .
On 3 Sept 1939, Britain declared war on Germany.

All this time, Britain had been preparing for war, and - in September 1939 - was much more ready for war than in 1938. This was not a pressure on Chamberlain, but it meant he could go to war if he needed:
1 December 'National ' of who would do what if there was a war.
3 January 1939 Britain strengthened the navy and (production of planes increases to 400 a month).
15 February Defence spending increased to £ million. A quarter of a million free were given to Londoners.
29 March Army doubled.
5 April Act passed (to allow evacuation: on 31 August the first children were evacuated)
25 April Defence spending increased to £1,322 million.
1 May Military Training Act (introduced ).