18USA: The Railways of the United States of America

1. Not a 1830 variant — it's an expansion/application of 1817
Unlike most titles on this list, 18USA does not build directly on 1830: it requires the components of 1817 (or the equivalent full/standalone edition) and inherits almost all of its financial rules. Because of this, every way that 1817 already differs from 1830 (loans, short selling, hostile mergers) also applies here, amplified by a much larger map.

2. Map: the entire continental USA
While 1830 is limited to the Northeastern USA, 18USA covers the whole continental United States, supporting up to 7 players (above 1830's maximum of 6).

3. Corporate loans and interest (inherited from 1817)
As in 1817, and unlike 1830, companies can take out loans to pay for trains or upgrades, generating interest that rises as more debt circulates in the game. This mechanic does not exist in 1830.

4. Short selling (inherited from 1817)
Also as in 1817, players can sell shares they don't own, betting the price will fall. In 1830, a player can only sell shares they actually hold.

5. Mergers and hostile takeovers (inherited from 1817)
18USA keeps 1817's system of friendly or hostile mergers and acquisitions between operating companies, a mechanic absent from 1830, where public companies can never merge with or absorb one another.

6. Randomized map and private companies every game
Unlike both 1830 and 1817 (fixed maps), 18USA randomly selects which private companies enter play (roughly 15 out of about 30 available) and randomizes the value of several off-map areas, so every game presents a different scenario.

7. City subsidies to incentivize less attractive routes
The game introduces specific subsidies to encourage founding companies in locations that would otherwise be economically unattractive. This incentive mechanism exists in neither 1830 nor 1817.

8. Modified train manifest and exporting compared to 1817
18USA adjusts 1817's train manifest (for example, adding extra 3-trains and changing which trains get exported — removed from the game — as phases advance) to fit the pacing of its much larger map.

9. Even higher financial risk than 1817
The combination of loans, short selling and hostile mergers from 1817, applied over a much larger map with randomized setup, makes 18USA one of the riskiest and least predictable titles to compare against 1830, which by comparison is the most conservative game of the series.

10. Designed for groups already experienced with 1817
Because of its dependence on 1817's components and rules, 18USA is best understood as a "large-scale expert mode" for groups that already know 1817 well, rather than as an entry point coming from 1830.

18USA — Schematic summary (vs 1830)

SETTING

• Requires 1817's components; inherits its financial ruleset
• Continental USA map, up to 7 players

FINANCES (inherited from 1817, absent in 1830)

• Corporate loans with variable interest
• Short selling of shares
• Mergers and hostile takeovers between operating companies

WHAT'S NEW IN 18USA

• Random subset of private companies each game (~15 out of ~30)
• Randomized off-map area values each game
• City subsidies to incentivize unattractive routes
• Train manifest and exports adapted to the larger map