Short answers, pulled from the story.
Athens introduced trial by jury and free speech alongside new markets in the 4th century B.C. Xenophon wrote the first document describing how these reforms sustained a self-sufficient city at public expense.
Producing less valuable coins to fund military expansion eventually caused the Roman Empire economy to collapse. Society retreated back to the countryside and returned to barter systems following this economic failure.
England transitioned from mercantilism to liberalism during the Industrial Revolution when individuals gained more political power through increased profits in international trade. These groups influenced political institutions to grant tools for further development.
Culture and history explain why some countries perform differently despite similar starting points. Many changes still lie in the future for these emerging democracies as they navigate their unique contexts.
The level of development measured as per capita income determines democratic survival probability. Years of schooling of an average citizen greatly elevate the chance a democracy will survive while income and education impact independence though their correlation remains strong.