Munich is the pivot in the stalemateline that goes across the board. In this example, Munich is held by French forces.
If France orders:
A BUR Support MUN
A RUH Support MUN
A KIE Support BER
A BER Holds
A MUN Holds
Italy will not be able to capture Munich, and can't capture Berlin with SIL and PRU either because of the support coming from Kiel.
Only with some help from the North, the line can be broken. Alas, in the above example we see a Russian Fleet waiting in Bal, which could change the game around by first giving Berlin to Italy, which will turn Munich into Italian hands soon after...
Note that Munich can also be held from the South, as in the next example:
These moves effectively hold of a French attack of:
A BER - MUN
A BUR S BER - MUN
A RUH S BER - MUN
A KIE S BER - MUN
Which would end in a 4:4 stand off. Again, because of the impenetrable Switzerland, the key provinces become Prussia and the Baltic Sea. Only if a change occurs around Prussia, Munich can change hands.