Thank you Noah Webster?

"…what Webster wanted to do was make English spoken and written in America different in many ways from English spoken in Britain. When he did this, America wasn't getting along too well with Britain-after all, we had fought a war to become independent not long before! So, in his dictionary of American English-the first of its kind-Webster decided to change many spellings. One of the most obvious was to take out the u in words such as honour and behaviour. He also switched the re in words such as theatre and centre."

Excerpt above is from page 261 - Words Their Way - Word Study for Phonics, Vocabulary, and Spelling Instruction

(Donald R. Bear, Marcia Invernizzi, Shane Templeton, Francine Johnston)