Final answer:
The Qin dynasty, established by Emperor Qin Shi Huang in 221 BCE, was the first to unite areas of modern-day China, creating a centralized imperial system and standardizing various aspects to foster unity.
Step-by-step explanation:
Among the dynasties listed in the question, the Qin dynasty was the first to unite areas that are part of modern-day China. Established by Emperor Qin Shi Huang in 221 BCE, the Qin dynasty lasted only 15 years but had a monumental impact. It was this dynasty that conquered and unified the various warring states of the time and standardized important aspects like currency, weights, measures, and even the writing system, which fostered unity and established an imperial system.
While the Han dynasty, which followed the Qin, also played a significant role in the expansion and development of China, consolidating much of what the Qin had started and lasting for over four centuries, it was the Qin dynasty that first accomplished the feat of uniting China under a single rule.