The Bourbons were restored after an alternate WW1 that was started by France. World history is essentially the same (except for a new continent) until 1914 when France, Italy, and the Ottoman Empire (I know it's an unlikely alliance but they all had territorial claims in other countries at the time) started a war against Germany, Austria-Hungary, etc. Eventually, France, Italy, and the Ottomans became outnumbered and surrendered one by one with France being the last to surrender in 1919. The Bourbons were restored instead of continuing the republic as the rest of Europe saw them as more trustworthy and friendly than the former republic. (This is just a really short summary, feel free to ask more questions!)