Off the top of my head, the big one was corporations, that give cities "stuff" (food, hammers, culture) at the expence of money in the late industrial / modern era. There were more scenarios (but none as good as the ones you will find here) and some tweaks to the tech tree.
[EDIT] and off
wikipeadia:
- Corporations: A new gameplay feature, similar to the religion feature, allows players to create corporations and spread them throughout the world. Each corporation provides benefits in exchange for certain resources.
- Espionage: Now available much earlier in the game, this expanded feature offers players many new ways to spy on opponents, stir citizen unrest and defend their governments secrets.
- Random Events: New random events such as natural disasters, pleas for help, or demands from their citizens will challenge players to overcome obstacles in order for their civilizations to prosper. Random events can also be beneficial, such as scientific breakthroughs or incidents that improve relations with a neighbor.
- Advanced Starts: When starting the game in any era, this new option allows the player to purchase components for an already-developed nation.
- Expanded Space Victory: Obtaining a space victory is now more difficult and requires more strategy and decision-making than before.
- Expanded Diplomatic Victory: It is now possible to achieve diplomatic victories much earlier in the game, and to defy resolutions.
- New Game Options: Beyond the Sword offers various new game options, like new world-types and the option to play any leader-civilization combination.
New content includes:
- Ten new civilizations and leaders (Babylonia, Byzantine Empire, Ethiopian Empire, Holy Roman Empire, Khmer Empire, the Mayans, Native Americans, Netherlands, Portugal and Sumer)
- 6 new leaders for existing civilizations (Abe Lincoln, de Gaulle, Boudica, Darius I, Suleiman the Magnificent and Pericles).
- 25 new units, 18 buildings and new technologies added primarily to the late game.[10]
- 11 new scenarios.[5]
- Six new Wonders of the World.
- New diplomatic resolutions through the United Nations.
General changes:
- Improvements in AI (Artificial Intelligence) for harder games across all difficulty levels. The AI player will attempt more ways to win than before. It is also better at warfare (particularly naval operations) and economic management.[14]
- Early-game units now have different regional art styles and motifs.
- Colonies can split off from their motherland to form new civilizations if maintenance costs get too high[15]
- The foreign advisory screen has been overhauled.[14]
- Beyond the Sword includes some material from the previous Warlords expansion pack, specifically the core game features, but not the Warlords scenarios.[14]