Final answer:
The demand for plain language began centuries ago, though a significant formal initiative was the Plain Writing Act of 2010 introduced by President Obama.
Step-by-step explanation:
The demand for the use of plain language dates back to well before the beginning of 2000, and even earlier than the early 1900s. In fact, the push for clarity in language has existed for centuries. However, a notable formal push for plain language in the United States occurred when President Barack Obama introduced the official Plain Writing Act of 2010. This act, adopted by Congress, aimed to improve government communication by promoting clear and understandable written content in laws and regulations, enhancing public access and comprehension.