for the most part a marathon is pack running, which has many aspects that you can compare to politics. for example the overall pace - if you think you can outsprint the pack, it's better to force a slower pace, and the reverse if you think you're gonna get outsprinted, force a faster pace or create separation.
in particular, if there are multiple runners from one country, they can/will take turns running in front of the other. this allows them to share the cost of breaking wind and creating draft, allowing the other to coast. if you have this kind of relationship you conserve energy which is sort of important when you need to run 26.2 ~4:40 miles in a row.
Run an 800m by yourself and then with your friend who's really into running. You'll do better the second time since you'll push yourself to be as good as he/she.
I'm still kind of in the dark. Are you saying that during a marathon there will be some "sacrificial" runners (I think they're called "rabbits")? That's like playing in a team, they're not really opponents.
You can't interact with the real opponents, as far as I know.
2. Different runners have different strengths. Some have a stronger kick at the end of the race, some have a weaker kick but can maintain a higher pace.
One example of how this can play out in a marathon (and, to a greater extent, in something like the 5000) is that a runner who has a faster overall potential but a weaker finishing kick wants the pace to be run at a higher tempo. However, if the runner tries to do this unilaterally, weaker athletes may be able to draft and use the physical and mental benefits to hang on, before winning using their kick.
However, if there are multiple endurance oriented athletes, they're typically more able to enforce a higher tempo throughout the run that will drop those athletes that have a stronger kick.
You'll often notice this in the 5000, where the winning time might be well below the personal or seasonal bests of many of the participating runners. Tactics prevent them from running their optimal race, and then a stronger kicking runner wins.
rabbits are generally used for time trials/record attempts. if a runner wanted to try for a 4 minute mile, they would have a rabbit run 2 or 3 laps evenly, at slightly better than 4 minute pace (say 800 in 1:58 or 1200 in 2:57). this allows the other racers to draft off the rabbit, as well as focus on running even splits so they have as much energy as possible for the final sprints.
rabbits in marathons are pretty rare (to my knowledge?) though
