The word allegaban is the imperfect form of allegar in the third person plural.
See the full allegar conjugation

allegar

En la reunión se propuso que se celebrara una conferencia internacional sobre las dificultades en relación con la devolución y la restitución y sus posibles soluciones y Grecia se ofreció a acoger esa conferencia si se allegaban fondos suficientes.
The meeting proposed an international conference on return and restitution difficulties and solutions, and Greece offered to host such a meeting if funds were made available.
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