I do believe that we are not mere teachers of the English language but also of the cultural background of the nations who speak it. That is why I think it is good to mention at least one personality, historic event, etc. at the beginnig of the lesson. To think of a warm-up activity that will be both appealing and instructive. I suggest to use what I have called: "Guess: Who? When? Where? Why?' I've noticed that students love guessing and they always enjoy this activity. With the help of modern technology a teacher may make it even more interesting.
The choice of the topic is up to the teacher. As there are various important personalities and significant events, the teacher can find the one wich will fit his/her lesson goals.
For example while focusing on modals why not first do this kind of guessing?
Students enjoy it. Depending on their level of proficiency you can challange them to look for other modals in Barack Obama's Speech in the New Hanpshire presidential primary. Ask them to compare them. What kind of meaning do these modals convey? If you have classes with beginners just let them say what each can do. You CAN think of any activity you like and which will help your students better assimilate the new material.