Complex sentence: They were descendants of old Bohemian/Czech Unity of the Brethren, extinct in Bohemia after 1620 due to forcible re-Catholicisation imposed on the Czech lands by Habsburg emperors, who in 1722 had found refuge in Saxony on the estate of Nicolaus Ludwig Count von Zinzendorf.
Split into simpler sentences: They were descendants of old Bohemian/Czech Unity of the Brethren, extinct in Bohemia after 1620 due to forcible re-Catholicisation imposed on the Czech lands by Habsburg emperors. These church members had found refuge in 1722 in Saxonym on the estate of Nicolaus Ludwig Count von Zinzendorf.