On Warlord I find the tactic that works best is aggressive expansion very early in the Game. Make Settlers first and move your boundaries out as far as is practical. Once Barbs are about to appear start making warriors to defend. Quick city builds are the key!
when you see barbarian already outside undefended city border, its almost always too late to build defense... (ok, whip can work, but new city almost never will have enough population to do that)
More important is to "take control" over barbarians by placing units around free land to stop barbarians birth as much as possible (it cost something, but its cheaper than just building strong defense). That give you time to settle something else 1st before settling this area.
Using this strategy in current game - had island for ~10 cities, but also 3 nice small islands near capital (I built Great Lighthouse, thats why small islands was nice).. So I fog bust big island with some 8 units (chariots/warriors, even worker can be ok if place near some city) and settle all 3 small islands to get best incomes from trade routes and was able to leave cities undefended for short time until city start getting unhapiness from "not having a defense".. After that I was able to build without worry about barbarians and same time getting best income I could get
For fast expansion best is to make 2nd city (with great food/production resources.. fish, corn, copper or something like that) as settler production city - chop 1st settler at size 1, grow to size 2, next settler, again grow 1 size up, next settler, when at happy cap, build settlers there as long as you need

3rd, 4th city - commerce from cottages, 5th - military city.. after that.. just whatever need and is available.. (capital city usually has something else to do.. some sweet wonder.. or some building.. or units for attack

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