Today is the day that the Reinheitsbegot was signed into law back in 1516. We understand its implication, that beer be made of three things water, barley, and hops (yeast was added in later, after it was discovered). But we tend to forget about the why.
Before hops were fully accepted (even used for that matter) beer was made with a mixture called gruit. This gruit was a mixture of herbs and spices that served the same purpose that hops serve today, they help to balance the sweetness of the sugary wort. The problem of this came with what brewers were using. Gruit could basically be comprised of almost anything from poisonous materials to psycotropic drugs.
In an effort to protect the populace the church controlled gruit using it as a way to not only control what went into beer production but also to tax the brewers. The church's strangle hold on gruit that helped to slow the acceptance of hops in Britain. You see it wasn't just Germany that had issues with what brewers would use in their brews.
In Britain, this is the time of Henry the 8th. During his time he broke down the power of the Catholic church in Britain (though for other reasons). Think of the implications this has for brewing. At this time beer is still much safer than water to drink.
This is all during a time of much political and social turmoil. The Duke of Bavaria enacts a decree, the Reinheitsgebot, to ensure that wheat is saved for bread (people still need to eat). It also set the price that can be charged for beer and put in a provision for the possibility of a short harvest. This was also to protect the populace against beers that went bad during the summer months. Mars biers or march beers were brewed stronger to lager over the summer and ensure that they had good supplies during the dry months. It wasn't until we understood the work of yeasts and found how to control fermentation tempertures that summer brewing became safe.
When we look at where we are now, we see that in the US with a bit of a different beer history is now embracing wide ranging ingredients. This, of course, is in answer to the effects of our own version of the Reinheitsgebot (or more exactly Prohibition). Prohibition was an effort for a different form of purity. But as is found throughout history when you enforce strict laws, people will find ways to thumb their nose at authority. The rise of speak easys and bath tub gin was just such a rebellion.
Enough of this, its time for a pint...