Global Country Establishment Dates Research

I need a well-sourced reference file that shows, for every sovereign country in the world (Please confirm exactly how many Countries there are in the world), the dates each country and all its states, providence was first established and the date it took on its present form, plus the same information for each of its current states or provinces. I am after both historical and current dates, so the file should capture founding events (earliest kingdom, colony, or declaration) alongside today’s legal or constitutional status.

Please compile the data into a spreadsheet that includes:
• Country or subdivision name
• Founding / first-recorded establishment date
• Date of its latest status change (e.g., independence, federation, constitutional reform)
• Brief note defining the event referenced
• Source citation with a live URL or full bibliographic reference

Use reliable, publicly verifiable sources—official government archives, recognised historical databases, or reputable academic works. Where dates are disputed, note the range and cite all positions.

Deliver the completed spreadsheet and a short summary (one page is fine) that explains the methodology you followed, any conventions you adopted for ambiguous cases, and a bibliography of key sources.