John Gill Commentary 1 Kings 16:11

"And it came to pass, when he began to reign, as soon as he sat on his throne, that he smote all the house of Baasha: he left him not a single man-child, neither of his kinsfolks, nor of his friends." — 1 Kings 16:11 (ASV)

And it came to pass when he began to reign, as soon as he sat on his throne

Perhaps the very first day.

that he slew all the house of Baasha ;

His whole family, all the children that he had, that there might be none to make pretensions to the throne.

he left him not one that pisseth against a wall, neither of his kinsfolks nor of his friends ;

Not any that might avenge the blood of his family, that might have a right or inclination to do it.