For England I want to say the crossover is about 150 years ago, could be 200, from memory. France & Germany a generation or two later, most other places later still.
The US frontier may well be different -- having almost infinite land meant it could sustain rapid expansion for a long time. I know that New England & Quebec had something like a doubling per generation in total a bit earlier, from say 1650-1800. Which was unprecedented, I don't think any other pre-industrial civilisation got close. (Mathus had the numbers and was suitably impressed.)
(Bear in mind that number of siblings looking backwards is a different measure to number of offspring looking forwards -- 2 kids/parent on average is perfectly compatible with everyone having 3 siblings, as long as they have some childless aunts.)
The US frontier may well be different -- having almost infinite land meant it could sustain rapid expansion for a long time. I know that New England & Quebec had something like a doubling per generation in total a bit earlier, from say 1650-1800. Which was unprecedented, I don't think any other pre-industrial civilisation got close. (Mathus had the numbers and was suitably impressed.)
(Bear in mind that number of siblings looking backwards is a different measure to number of offspring looking forwards -- 2 kids/parent on average is perfectly compatible with everyone having 3 siblings, as long as they have some childless aunts.)