Gustav Stresemann was an interwar German statesman who served as Chancellor in 1923 (for a brief period of 102 days) and Foreign Minister 1923–1929, during the Weimar Republic. He was co-laureate of the Nobel Peace Prize in 1926. Stresemann was a complicated political figure, but was regarded by many as a progressive modern politician. However, in OTL 1929, he suffered a deadly stroke. His death cut his perspective political career short.
The POD is simple: Stresemann survives the stroke, eventually gets better and returns to German politics to score new victories he never had.
The timeline goes on to explore the consequences, first in Germany and then, as the ripples expand, across the world. Despite the fact that Stresemann helps stabilize the Weimar Republic and averts the rise of Nazism and other German extremist movements, Germany's post-Imperial history is not all sunshine and rainbows, by any means…
The story is told partly as third-person vignettes from the altered world, partly in an authoritative and impartial history-book tone, the whole sprinkled with footnotes which are sometimes purely informative but just as often display the author's characteristic sarcastic wit.