Английский язык!? Я запуталась!

В какое из предложений вставить due to, а в какое so
(вместо точек) .

1) The frontiersmen left the known of the Old World for the unknown of the
New,……………………………… they were risk-takers.

2) …………………………………………the frontiersmen left the known of the Old World for the
unknown of the New, they were risk-takers.