Like above posts said, the original idea was based on the conceptual framework inherited from classics like The Seven Cities of Gold, Uncharted Waters and Colonization:
You play an explorer sponsored by a European Home CIty. Your exploits in the Americas win you Fame, which convinces your European patrons to invest more manpower and supplies in your venture. Originally, AoE3 was planned to have a single player Grand Conquests mode, comparable to similar meta-campaigns in Rise of Nations and Dark Crusade, making full use of this explorer-colony-home city dynamic.
However, it is also clear that during development, AoE3 and the concept of XP had become decoupled from this very specific scenario, turning far more nebulous and therefore flexible for game developers to use. The conceptual break was drastic enough that the XP resource we have in AoE3 is a new resource type added separately from the now-unused Fame, suggesting there may have been a period where they coexisted side-by-side.
Each expansion pack has further broadened what Experience Points entail. In addition to being generated from economic and military activities in the player’s domain, they now come from:
- International trade (trade routes);
- European religions (Mosque trickle in original, Church trickle in DE);
- Intellectual movements, specifically early economic theories (Mercantilism in original, Bullionism in Spanish Consulate);
- Grand native American festivities (New Year Festival big button);
- Social connections (Gift Ceremony in TWC, Cooperation tech in DE);
- Asian religions and eco-agricultural management (Shrine and Sacred Field animal trickles, Meditation tech in Zen Temple);
- Book imports (XP crates - Pile of Books);
- Education and culture (University);
- Spiritual purification (Catharsis tech in Athos Monastery).
And can be spent on:
- Supplies and manpower;
- Economic infrastructure;
- Technological advancements;
- Social reforms;
- Military and civilian training;
- Traditional social institutions;
- Discovery or obtainment of natural resources, raw materials;
- and so on.
With such wide-ranging themes, it seems wise to not bog down XP with specific concepts like fame, scientific knowledge, or spirituality. Rather, I think it’s better to connect XP with the overarching themes of early modern history: collision and exchange of cultures and materials; global movements of human, animal and plant populations; waves of new thoughts and ideas; epoch-making social shifts. AoE3’s period is one where the earth became truly interconnected, when humanity’s ways of life changed.
This way, XP can then be seen as an abstraction of social developments, a sum of the subtler forces of history, unlike the raw materials we collect and troops or facilities we build. When these forces coagulate underwater and break through the surface ice into visible historical events, these are the shipments.
For comparison, Colonization also has two abstract cultural resouces: Liberty Bells, which are the colony’s growing intellectual vibrancy and independence sentiments, and Crosses, representing religious activity. AoE3’s XP may encompass them, and then far more.
Line infantry formations and skirmishers. Devastating heavy cannons and dashing hussars. The constant reforms in military science and institutions, represented by the home city cards.
Sweeping through old empires with new armies of revolution. AoE3DE is packed with content I love.
-- A random forum post from 2021