Simplify the following text for a Grade 9 native English-speaking person.
Original: Christadelphians ' ( a word created using Greek which means Brethren in Christ â '' `` brethren in Christ '' ) is a Christian group that developed in the United Kingdom and North America in the 19th century .
Simplified: The Christadelphians are a Christian denomination that developed in the United Kingdom and the United States in the 19th century . Other names for them include Brothers of Christ and Christ 's Brethren .