Which factor played the most important role in the expansion of economic connections between countries since the mid-20th century?
A. International efforts to protect the environment
B. Advances in technology
C. Rapid inflation in most countries
D. Reduced trade between neighboring countries

Advances in technology

Explanation:

Advances in technology is the single most important factor in the expansion of economic  connections between countries since the mid-20th century.

Since the mid-20th century, the gap between nations is being gradually covered by technology. This has facilitated ease of doing business and have reduced the communication gap and as well as closed up the economic gap between nations.

All these have greatly contributed to the expansion of economic  connections between countries since the mid-20th century and is a great boost to global trade.