I introduced Kodak who was 2 at the time to his little sister Kamari and all hell broke loose.
Kodak was so spoiled because I thought he would be the only dog but eventually he needed a playmate. So I opted for my little girl & she is so sweet. He use to be such a good boy, then he would jump on her and fight at the spur of the moment. She is smaller than him but she has been defending herself from day one.
I literally had to seperate them at one time. Well, she will be a year old this month and he is a lot better once he saw she will fight back. But at one time during the first 3months, I thought I was going to have to give him to my mom.
I did everything the same, and gave them both attention, but he didn't want her playing with his toys or nothing.
He is neutered and I thought he would act so much better back then. Now he's ok with her, they do play 60% of the time, the other 40 they are duking it out. LOL! He had to come around but hopefully you'll have better luck than I did. I love them bunches though.