A very interesting game. Thanks aelf for working so hard and presenting all this to us in such a clear way. It is very much appreciated.

You've proven it is tough to win at this level and that this series really is a challenge worth reading and discussing.
I think that your basic plan for the end game was sound, except Louis screwed it up

, and so it was too much to do in too short a time. If he had not attacked and disrupted your preparations for war then you could probably have beaten Brennus. I am not sure how you could have prevented Louis attacking in this way except by yielding to his earlier demands for tribute. Maybe changing to Free Religion would have helped.
In 1848 you were certainly running what I would call a late game SE and it was like that throughout most of the game, with Representation, Mercantilism and SoL contributing lots of beakers and GPPs. You produced 17 GPs of various sorts which is not bad going.
However if we look at the Financial Advisor screen we get:
100% Research 1059, Culture 315, Gold 67, trade 10, Exp 226
shifting the slider to 0% research
0% Research 262, Culture 315, Gold 790, trade 10, Exp 226
This indicates that there is a very large amount of commerce in the economy (due to many captured towns) At 100% the commerce gives 797 beakers and at 0% it gives 722 gold. The total size of your economy at this stage is 1126 (gold + beakers) at 100% and 1051 (gold + beakers) at 0%, so at 100% we have 797 from 1126 or about 70% of the economy is from commerce. You are running mainly engineers in 1848 rather than scientists or merchants so that would skew the results somewhat. My analysis doesn't take account of the GPPs which can also be counted as additional beakers from the specialist side of the econiomy (only if they produce a GP). However, I have to conclude that in 1848 the economy is firmly a hybrid or HE (as many late game SEs become).
A few technical points: Researching Biology would quickly have paid off in extra food production. You are working a large number of farms. Several cities (e.g. Munich and Philadelphia) are short of food and working plains farms is weak without Biology but more than adequate with it. The main reason Louis and Brennus are so far ahead in population and production is Biology. My attitude to this tech is coloured by my aversion to Scientific Method when I have the Great Library to lose, but for a farm based economy, like you clearly have here, it works wonders roughly doubling the productivity of plains and grassland farms. So for a late game SE it is essential.
Another technical point. The 3 cities on the southern border (Boston, New York and Washington) would have benefitted more from applying cultural pressure to Brennus's tiles. That would have helped more than the few extra troops they produced. A Buddhist stuppa in Washington, for instance, only costs 150 hammers (with 100% bonus) which is the same as the artillery currently building. Obviously cultural preparations take time to work on the tiles so those cities should have been made ready for the coming war against Brennus as soon as they were captured.
I hope to replay some parts of the late game to see what might have happened in an alternative universe. But I am not an immortal level player so it is just to satisfy my curiosity. I'll report anthing interesting in this thread for further discussion. I think this game might be winnable as Melior Traiano showed in his alternate ending (he came close to winning) but probably not by me
