Which historian argued in the 1910s that slavery was a generally benign institution where slaveholders cared for happy slaves?

Ulrich Bonnell Phillips is the historian who argued in the 1910s that slavery was a generally benign institution where slaveholders cared for happy slaves.
He is the first historian, his works of South and Southern slavery attracted the attention and creates controversy of some historians. Today, he is remembered as a conservative, proslavery interpreter of slavery and slaves.