almacenasen
-they stored
The word almacenasen is the imperfect subjunctive form of almacenar in the third person plural.
See the full almacenar conjugation

almacenar

Ello no obliga a imponer una prohibición total de esos materiales, pero se podría instar a los Estados a que impidiesen que las personas y entidades incluidas en la Lista los obtuviesen, controlasen, almacenasen, empleasen o procurasen conseguirlos.
This need not require a total ban on such materials, but States could be urged to prevent listed persons and entities from obtaining, handling, storing, using or seeking access to them.
Want to Learn Spanish?
Spanish learning for everyone. For free.
SpanishDict Premium
Have you tried it yet? Here's what's included:
Cheat sheets
No ads
Learn offline on iOS
Fun phrasebooks
Learn Spanish faster
Support SpanishDict