What was the first arena of religious conflict in sixteenth century europe?

The first arena of religious conflict in sixteenth century Europe was THE HOLY ROMAN EMPIRE.

The Holy Roman Empire was composed of different states that have its own European powers, regional powers, religion. It became the first arena of religious conflict because other states wanted to extend their power and religion to its neighboring states which resulted to a series of wars which started in 1524 and ended in 1648 with the Peace of Westphalia.  

Because broadest terms allows the law flexibility depending on changing society and circumstances.