Volvo Transmission Model and Parts Interchange

[Tim73]

I would like to thanks all the people supporting this forum. Without your resource and information, I would not understand any of the below I am going to ask. As soon as I learnt and experienced something I will help others to find solutions.

I would like to open this topic so Volvo Expert will educated Volvo lovers to understand and find solutions for problems may occur.

1) Since what year Volvo start using GM transmission on their car ?
2) List of transmissions model that use on EDM (European Domestic Manufacture), and Transmission model that use on USDM (US. Domestic Manufacture) ?
3) Is it interchange between car to car with in specs (torque ratio, Trans mount, Transmission control Module ) ?
4) Why do they have ECU, TCM computer and electronics parts made in Germany (Europe) and Transmission is Made in US (GM) ?
My concern is why NOT American made both Transmission and the controller together? Or let's the Europe done both ?

FIY: I am no Volvo expert nor Mechanic of any way, just a Volvo owner and would love to learn from experienced volvo owner, Volvo Expert, Volvo Engineers, GM expert,...

Thank you all