The mutual defence clause is in play for the first time, but there are limits to what member states must do to helpFrance has taken the European Union into uncharted territory by obliging the other 27 member states to come to its defence following the terrorist atrocities in Paris.Invoking article 42.7, a never used clause of the EU treaty triggering mutual defence among the 28 member states, Paris admitted it was struggling to cope with its foreign military commitments while beefing up security at home in the wake of the attacks, and asked the rest of Europe to come to its assistance.