Complex sentence: According to some historians, Napoleon's pro-Italian and anti-Austrian sentiments deterred him from intervening in the Austro-Prussian War on the Austrian side, thus allowing Prussia to gain sufficient strength to defeat France four years later in the Franco-Prussian War.
Split into simpler sentences: According to some historians, Napoleon's pro-Italian and anti-Austrian sentiments deterred him from intervening in the Austro-Prussian War on the Austrian side. This allowed Prussia to gain sufficient strength to defeat France four years later in the Franco-Prussian War.