Global Coalition aims at protecting you from invaders. +7 Combat Strength is a decent number, as it will reduce the damage your units take by approximately 30%. However, the fact that this is one of the last policy cards unlocked in the game makes it really hard to use effectively. If your civic advancement is not far ahead compared to the technology advancement of your enemy, this card effectively just prolongs the agony: Giant Death Robots and Armies of Mechanized Infantry and Modern Armor can still make quick work of an obsolete army, as it is incredibly hard to close the Strength gap between these units and those of previous eras. This card is most useful when you play for a Cultural Victory: with a massive generation of Culture, you can unlock this card a few eras earlier than your opponents, which will actually allow you to witness its efficiency.
Since the middle of the Twentieth Century, attitudes towards war between nations favor action by multiple nations agreeing to a common objective, rather than individual nations acting in their own interest. This system is assumed to represent a wider portion of the attitudes of people at large, and thus is more justified, should one believe that sovereignty rises directly from people. Successful global military coalitions have been formed by both the United Nations and by blocs of nations working in concert in a variety of armed conflicts. Junior partners in these coalitions may sometimes be induced to join a “coalition of the willing” through incentives through the senior partners in cases where the moral basis for the coalition is more ambiguous.