Um isn't a centralized area supposed to be crowded?
So since there would be many defenseless people there I think Pokemon would cause thousands of casualties in a matter of hours and till the army is ready for a counter attack ,Pokemon would have destroyed everything there.And of course we don't suppose that ALL Pokemon would 'fall' in one country. There wouldn't be enough place for us all. They would be spread around the world.
Also see this image :
http://my.opera.com/Thm-kirby/albums/showpic.dml?album=603478&picture=8275876
See? Now just remove from there those 3 beasts and put Dragonite instead. Yeah, Dragonite is capable of handling the weather and everything related. So just by this ability Dragonite would cause major destruction. So many thunders,hurricanes,tornadoes,earthquakes and tsunamis(around 6-7m waves I imagine) and so many earthquakes and blizzards also by every Pokemon. I mean they have the nature on their side.Every natural disaster is accessible to them through attacks or Dragonite's family ability.
There are also Psychic types who can stop every bullet or cannon fire in mid-air and throw it back,do basically everything they want with their minds and kill us easily.What about them teleporting our weapons or even tanks anywhere they want? Maybe in the ocean or anywhere far away? I imagine that any Pokemon able to learn Teleport could do that.
Steel types would be almost bulletproof and invulnerable.Not all Steel types but most of them.Also included: Cloyster(may not be a steel type but he is very durable)
Rock.Steel and Ground types would level everything with their powerful Earthquakes,Rock Wrecker,Earth Power etc and destroy entire cities and villages with earthquakes,rock slides,land slides(sand tomb) and other moves like stone edge,rock blast,fissure etc
Poison would poison and kill us all.Poison gas - poison the air.That's enough. Just this could kill us all by poisoning. Sludge wave,gunk shot,sludge bomb and sludge are very dangerous and powerful while Toxic would be deadly and inevitable.Also,poison our water sources.
Electric would cause major black outs and EMP that would shut down technology.How would we be able to fight them without any technology till the problem is repaired?Also electromagnetic explosions would wipe out many areas. Electric Pkmn would shoot electric bolts electrocuting us and even starting small fires from burning trees.They could summon lightning bolts from the sky to kill us all and cause thunderstorms.What else to say?
Ice Pokemon would freeze everything with Sheer Cold,Glaciate,Blizzard,Ice Beam etc
Fire Pokemon would burn everything down.
Water Pokemon would blast everything away with Hydro Pump/Cannon from humans to cars due to the sheer volume,pressure and power of the water. Surf would be basically a tsunami up to 7m tall.Pretty destructive right? Whirlpool would swallow ships and submarines etc
Flying types would not only attack us fiercely from above but also whip up so powerful hurricanes,tornadoes,gusts of wind and whirlwinds ripping everything in their way.
Grass would be quite dangerous too.All those pollens.Sleep Powder would make a whole army fall in a rather deep sleep, Stun Spore would paralyze us and Poison Powder would obviously poison us badly and kill us.Seed Bomb would be hard explosive nuts.You get the picture. Also, they could summon Solar Beams from the sky scorching everything.Power Whip would be powerful enough to break all your bones and Frenzy Plant would destroy a whole army easily shredding everyone.Leaf Storm and Petal Dance slicing everything and Razor Leaf doing the same job, but with less leaves and no wind.
Dragon type being the most powerful would just kill every thing moving. Draco Meteor would devastate cities.Dragons can pretty much control most elements so they destroy us. Hurricanes,Tornadoes,tsunamis,earthquakes,lightnings,blizzards,ice beams,fire etc They would kill us due tot heir powers but also their huge size and strength. Dragonite would control the weather and turn nature against us.
Ghost,Dark types would scare the hell out of us and kill us easily.Especially Ghosts. Fighting types would be like Hulk.Kick our butt. Bug types would be creepy and scary as hell.They would kill us easily.Huge bugs slicing and stinging us.Imagine scyther and beedrill.Or Pinsir and Scolipede.
Finally, Normal types would be the basic 'soldiers' of them. Hyper Beam,Giga Impact,Explosion,Hyper Voice would be very destructive, blasting everything away and destroying. Also many normal attacks are very powerful like mega kick/punch, double edge,take down. Even a Jigglypuff and Chansey would kill us easily.
What about now? Still humans win?