At Munich Britain and France ceded the Sudetenland to Germany (over the heads of the Czech government who knew it would leave them defenseless as that was where their forts were) in the (sincere) belief this would lead to peace (ie. the policy of classic appeasement). Germany's occupation of the rest of Czechoslovakia in March 1939 meant that no further pretence could be maintained that appeasement would work, hence Britain and France began to prepare for war and offered, an essentially meaningless, guarantee to Poland (who, it was clear, would be next in line for Nazi expansionism.) When the Germans invaded Poland later that year, the Western allies had no choice but to act on their guarantee and declare war, even though they did nothing to act in support of Poland, which was overrun within weeks.
Therefore the policy at Munich ('land for peace) served only to sell out the only democracy in central Europe in Prague and then to support a very nasty military dictatorship in Warsaw while managing to save neither from Nazi aggression and plunging the whole continent into war.
So, the Western allies did not 'acquiesce' in the annexation of the Sudetenland, they saw it as a constructive response to the 'problem' of Czechoslovakia; they were preparing for war from March 1939, not September; and they did not 'intervene' following the invasion of Poland, they essentially stood aside and did nothing for the next six months (an extension of the appeasement mindset in wartime).
Other than that, your history is spot on!