What does "then" mean in this case above?

But while idealists looked for the eternal and change­less in the realm of spirit, these materialists looked for it in the material world itself. And they found it in the ultimate material particle—the eternal and indestructible atom.

For such materialists, then, all changes were produced by the movement and interaction of unchanging atoms.

Materialism and the Dialectical Method (Maurice Cornforth)

What does "then" mean in this case above?

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