Verb (5-dan, る, intransitive)
1. to become stronger; to grow in intensity; to grow violent; to become worse
それでもやっぱり、不安は募る。Even so, the anxiety still grows.
Verb (5-dan, る, transitive)
2. to invite contributions, etc.; to solicit help, participation, etc.; to recruit (e.g. soldiers)
彼はそう考えて、民衆のなかから兵を募った。Thinking so, he recruited soldiers from among the populace.