Why did Bismarck want all the different German kingdoms to become one big country? How would that be a good thing for Germany?

There was a lot of fighting between the numerous German kingdoms and this made it possible for other European countries to dominate the area through political influence. He wanted a strong single German kingdom that could oppose this and prevent wars with France or Britain or similar countries that might work against them.

It made them stronger because it made a single economic zone for all the German kingdoms with shared history and a shared language which enabled them to develop rapidly instead of some kingdoms being stronger and some weaker. It also made it possible for them to oppose other great Kingdoms of Europe since they were still feeling angst after Napoleonic wars.