In response to the suggestion above, here's an answer about why you might use a recumbent on a world tour.
As Neil Fein says, comfort on the bike is a huge issue on longer rides. A recumbent offers you the "lounge chair" position which is much more comfortable than any upright bike. At the same time, you can also choose a more upright position than most uprights offer, so you see more. Instead of your back sloping forward and making your natural eye-line point at the road by your front wheel, your back slopes the other way and your head is naturally vertical. It's hard to describe the increased comfort because it sounds exaggerated. But I can finish a long day on a recumbent bike and feel tired, rather than really, really sore ... oh, and also tired. All the stuff about a good saddle, cycling knicks, creams, inspecting your crotch every day, caring for saddle sores... it doesn't happen on a recumbent.
There is more variety in recumbents in many ways, but the most common is a short wheelbase bike:
That's Mattheui's bike in Bolivia after some months on the road http://tourdumondeenbent.free.fr/en/index1024_cadres.html In my experience most recumbents end up looking like that after a few months on the road. It's just too easy to strap stuff on and keep going.
All the features listed above are present - considerable load carrying capacity, 26" wheels, V brakes, derailleur gears and so on. It's a bike that can be fixed easily with parts that are readily in most of the world. The features more common on a recumbent are the rear-view mirror on the handlebars, the lack of front panniers, the tubes enclosing the chains and the stick-as-stand. Note that the wind resistance of this bike is probably greater than that of a similar upright bike, so it lacks that advantage that a recumbent would usually have.
There are other choices. If you're not doing much riding on unsealed roads a recumbent trike offers greater stability which saves energy and lets you pay more attention to the scenery. The disadvantage is that a trike has three wheel tracks, so it's harder to avoid bumps (which is an issue for recumbents in general as it's hard to lift your weight off the seat). A long wheelbase bike is more stable than a short wheelbase bike, and it's easier to mount and dismount a loaded bike. As you might expect there is a wide range of strongly held opinions on these questions within the recumbent community.
Personally I have toured on both recumbent bikes and trikes (as well as uprights). I'm unlikely to tour on an upright again, due to the advantages of a recumbent. I did 5Mm or so on a recumbent tandem trike from Broome to Perth, and that was very stable with a huge load capacity, but slow on the hills and gravel. My SWB bike has an extra-long back rack, allowing me to carry a pro camera kit as well as touring load, and I've ridden that on a number of shorter tours (2-3Mm each). I have also toured on a SWB low racer (silly, but fun) and a recumbent four wheeler, which is as slow as the tandem but has a ridiculous load capacity (at one stage I had about 120kg on board when someone I was riding with had problems. So I strapped their Bob trailer to the top and kept going). The problem with the quad was that a chain, cassette and crankset lasted 3Mm before wearing out. All of those bikes had 406 wheels (BMX size), disk brakes on all wheels and various custom-made accessories (I make my own panniers, for instance). The bike has a Rohloff, and after the first tour so does the quad. Here's a shot of my tandem and trailer in Broome
(That's Mattheui's bike in Bolivia after some months on the road http://tourdumondeenbent.free.fr/en/index1024_cadres.html)