NYT has a good explainer on
what's happening with the sudden political crisis in Germany over migrants.
Cliffs: Merkel's party is in a governing coalition with a more conservative party that's dominant in Bavaria, and the interior minister (who's from that party) threatened to blow up the coalition if Germany didn't do something about migrants, because he's worried about his party getting outflanked from the right at home in Bavaria. To compromise, Merkel said Germany would set up camps along the Austrian border to house and review migrants' status, which is significant because it means policing a border that according to the Schengen area should be open.
There's a huge amount of symbolism in Merkel, one of the more visible faces and proponents of the EU, compromising away some of its core values, and would likely start a trend of some of the more anti-EU member states saying "**** it, if Merkel can do this, why aren't we?"
Article has a lot more details.