The correct answer is B.
The systems of alliances that had been constructed, through which the different nations set up relations with some partners, aimed to keep a balance in power forces across the continent. In turn, it managed not to set a balance but to polarize positions, to create to opposite factions.
Most countries had been aligned with one of the groups therefore, when a conflict was triggered, every country participated on it, embodied in a group of allies. The two world wars are the evidence of this.
