Removed for speculation, and poll type question.

You might want to pose this question to /r/historicalwhatif.

Per the AskHistorians Subreddit Rules: "Questions should be about what did happen, not what could have happened. Questions of that type should be posted in r/HistoricalWhatIf."

FYI, there are going to be a lot of answers. :)

The Battle of Vienna in 1683 in which the Holy League (Poland and allies) and the Holy Roman Empire stymied the Ottoman Empire from advancing into Central Europe.