@TBG07 first the non-country specific portion ---- ( a ) as an expat, you will file form 1040 as normal , you may also need to file a form 2555 ( establishing foreign tax home ) and thus be able to exclude your foreign earnings from US taxes ( up to an yearly limit ); (b) you will still be able to claim all the benefits ( credits / deductions etc.) just as if you were residing in US of A; (c) as a citizen you do not have to visit the USA once a year but you cannot be in the USA ( for any purposes) for more than 30 days out of a 12 month test period to comply with the Physical Presence test ( form 2555) in order to preserve eligibility of excluding foreign earned income. Since you have been abroad since 2014 and never had to file form 2555, and exclude your income, this may be new to you -- for any earned/self-employed income from here onwards . You did not have to file form 2555 because your employer was US govt. -- it was not foreign income.
Now for the country specific part ---- generally he tax treaties between USA and your resident country would exclude that country from taxing US govt. paid pension. Also social security from the USA may come under a totalization agreement. Suggest you read up the tax treaty --- > https://www.irs.gov/pub/irs-trty/spain.pdf
and https://www.treasury.gov/resource-center/tax-policy/treaties/Documents/Treaty-Protocol-Spain-1-14-20....
Hope this helps. Is there more I can do for you ?
