The OP is likely a troll, but I'll respond anyway. Why would you use marines to attack a fortified city? Marines are meant to be used for amphibious attack and as a counter to machineguns and artillery. Use infantry (who are cheaper) and have a bonus against gunpowder units.
As for minor differences and similar play styles, not true. While differences are not earth shattering at first glance, they are substantial and influence your play-style a great deal. For example, the Dutch will be excellent on a map with large bodies of water (especially a new world type of maps) and benefit from a peaceful game. If you are playing a land map with Dutch, you will mostly likely lose to an aggressive opponent (ie. Mongol/Egyptian neighbour with horse resource), especially if you have no copper (or iron, but it might be revealed to late to matter) but you might survive if you play with Mayans (Holkan doesn't require copper or iron). Good example are the Romans. You will usually want to rush to iron working, find iron resource and pump out Praetorians (they pretty much own every other unit until crossbowmen and longbowmen). If you have catapults, they own every unit until macemen. And that is a loooong time to be owned
You will rely on specialists to generate research (and great people) in games with Gandhi, while you'll look to earn as much gold from trade with Hannibal to spend on research or buy technology from others. You can also spend commerce income on espionage points to steal the tech and sabotage other players.
Traits and starting tech dictate the early game too (of course the starting position and resources are also important). Try to get early religion or get to bronze working and chop some wonders? Let your capital grow, whip some settlers and take the large area of the map? Try to get alphabet and trade techs? Go for library and get the early great scientist? Get to horse riding and take your neighbours cities? Oracle slingshot to Civil Service and massive bonus to your capital?
The graet thing in Civ 4 is that you can do any of these with any civilization, but "the few minor bonuses" make the difference between building the Pyramids or being left with 30 turns of hammers converted to gold (in other words wasted).
Tanks easily beat longbowmen in all but extreme situations. Given that longbowmen have 6 strength and tanks 28, plus the tanks have city raider promotions available it would take some huge cultural bonus to offset the difference.
Here's an example:
Let's say that longbowmen are fortified in a hill city, with 3 defense promotions. That's 25%(fortified) + 25%(hill) +25%(city defense) + 50%(hill bonus for archers) + 75% (defensive promotions) = 200%
Let's say that the city has a 100% cultural bonus. Tank has no promotions. That's 300% bonus for longbowmen. Longbowmen also have 1 first strike.
Attack strength = 28
Defense strength = 6 + 6*3 = 24
http://www.civfanatics.com/civ4/strateg ... lained.php
That means about 65% chance of tank winning the battle. And this is an extreme situation.
As to big stack of longbowmen "owning" stack of tanks with no defenses, yes, it could happen, if the numbers are something like 7:1 in favor of longbowmen (more if the tanks get to blitz first). Tanks cost 180 hammers, longbowmen 50 (plus the upkeep cost of a stack of 30-40 longbowmen every turn), so if you want to waste hammers, go ahead, "own" the poor tanks.
The key in Civ 4 is to have a good mix of forces in a stack (and a big enough stack). If you eliminate city defenses (cultural, walls, castle) by bombarding or sabotage (spy), "attack" units (swordsmen, macemen, tanks, all with city raider promotions) easily dispatch of defenders (even from later era, ie. macemen are still good against musketmen and grenadiers). If you do some splash damage and weaken the defenders and remember to bring medic promoted unit, the invasion will go even smoother
