The Spanish authorities opposed the referendum and claimed that independence is illegal. Catalans are not the only Europeans seeking independence. Some Bavarian people are demanding independence from Germany, while others demand greater autonomy. Germany's Federal Constitutional Court ruled: "In the Federal Republic of Germany … states are not 'masters of the constitution.' … Therefore, there is no room under the constitution for individual states to attempt to secede. This violates the constitutional order."
Germany has done in Bavaria what Spain and Italy, in its Veneto region, have done; it has upheld the integrity of state borders. There is an excellent article written by Joseph E. Fallon, a research associate at the UK Defence Forum, titled "The Catalan Referendum, regional pressures, the EU, and the 'Ghosts' of Eastern Europe" (http://tinyurl.com/y8dnj6s6). Fallon writes that by doing what it's doing in Bavaria, "Berlin is violating international law on national self-determination. It denies to Bavaria what it granted to the 19 states that seceded from Yugoslavia and the Soviet Union.