The Left Bank
The Left Bank is a decision available to France. It is available if Prussia exists and owns the to provinces Trier (In Rheinland) and Cologne (In Nordrhein). Prussia owns both provinces in the beginning of the game. Otherwise it requires that France has researched Ideological Thought. It cannot be taken if Prussia has formed North German Federation or Germany, so it must be used early in the game.
It reduces the relation with all states in Germany by 100, gives 4 infamy and 11 prestige and gives an acquire state casus belli to France against Prussia. The casus belli only lasts for 1 month, so war has to be declared immediately.
It is part of the chain of decisions surrounding the Rhine crisis. It leads to the Prussian decisions Die Wacht am Rhein and Niederwald Denkmal. The two decision will remove 7 infamy from Germany, but will not affect France directly, so one should not avoid taking the decision in fear of those two decisions.
During Napoleon's redrawings of the European map, the left bank of the river Rhine had been annexed to France proper. In 1840 France's Prime Minister Adolphe Thiers publicly stated that, in his opinion, the Rhine still remained France's natural eastern border. With the hardships of the Napoleonic wars still in living memory the statement caused uproar in Germany, sparking what would become known as 'The Rhine Crisis'