Question... why do you want to go national? I am amazed at the people who display interest in going national. Your organization is over 50 years old, it's already self suficient. If you want my advice, stay local. If you want the advice of others on my campus, stay local.
Why? Becauase at least at my school, locals have certain benifits:
1. You can vote how you like in IFC/Panhel without your national strong arming your vote on certain issues (we have had trouble with this in our IFC).
2. Dues are cheeper (all locals dues are 100-150% cheeper at duquesne). Overall it costs less.
3. No national convention bullshit to attend (which costs money).
4. You get the recogonition of a FOUNDER of an alpha chapter of a sorority/fraternity. This is probably the BIGGEST reason why.
5. Your national isnt trying to override the alumni board and tell it what to do...
6. You dont have consitutional limits placed on you (ie: you can write your consitution without having to worry about national clauses saying you cant do this or that).
7. It is a much more of a learning experience... you don't get the same amount of learning going on if you have national officers comin in and recruiting entire floors of dormitories for your group in like a week. (like one national on our campus did--our national made us do all the work by ourselves)
8. No Restrictions on Pledge programs... some nationals require that pledging be no less then 6 weeks... on average at duquesne, pledging is much shorter for the locals (and way more effecient, and less taxing on the group) then the nationals. One local's pledging is 7 days, one is four weeks.
The bottom line says: which would you rather be: your own organization that does what it wants, or an organization that is subservant to a national body.
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Now, if you wish to make your sorority a national one (ie: expanding from your campus). I think it's an AWESOME idea!
You can start by going to schools in the area and posting flyers and other things... schools which dont have greek systems at all are easy pickings... Charters are granted by the alpha chapter until there are enough chapters to warrent a national office being formed...