Why was the Old World covered in Earth? Mudflood? What happened in the last 300 years?

They call it Mudflood. Why were cities and buildings covered by feet or metres of earth and dirt. It means that there was no human activity for many decades? So what happened in the world in the 1700s and early 1800s? If you like my channel: ▸ Instagram: ▸ Patreon: (currently not posting new content) ▸ PayPal: ▸ Shop: ▸Facebook: ▸Twitter: