A little information about Herbert W. Armstrong
His unique doctrines and theological teachings, sometimes referred to by critics as Armstrongism, included the interpretation of biblical prophecy through the belief that the British and American peoples were descended from the lost ten tribes of ancient Israel and the requirement of observing Mosaic Law including the laws concerning the Sabbath, dietary prohibitions, and the Levitical "Holy Days".
The Sabbath and dietary laws were in existence before Moses, and the Holy Days are forever. After all, Yeshua commands us to commemorate His sacrifice, His death, every PASSOVER, and the Sabbath-keeping Church of God was founded upon the holy day of PENTECOST. Good thing those Jewish converts didn't fall for the religious lies popular today that blather they were all "done away!" (1 John 2:4, Titus 1:16).
Herbert W. Armstrong was courageously teaching the plain truth around the world, announcing the good news of the Wonderful World Tomorrow, the Kingdom of God that will soon be established with the return and reign of Christ.
The Plain Truth About Herbert W. Armstrong and the Worldwide Church of God
As far as the Israelite origins of the West, our Hebrew roots:
The Plain Truth About British Israelism
What is British Israelism and is it Biblical?