What was Grandpa's itinerary?

Question

Grandpa decides to take a multi-country tour visiting big cities

First he goes to LIBYA

Then to PERU

Then to BAHRAIN

Then to _______

Then to _______

Then to _______

Fill in the three blanks and tell me why

Answer 1

I believe Grandpa's complete itinerary is:

LIBYA, PERU, BAHRAIN, MARSHALL ISLANDS, ITALY, MEXICO.

Explanation: As @El-Guest found, Grandpa is:

Visiting capital cities where the last two letters of one city are the first two letters of the next: Tripo[LI] - [LI][MA] -- [MA]na[MA] (the capitals of Libya, Peru and Bahrain respectively).

There are several possibilities for the 4th, 5th and 6th cities on the list if this is the only stipulation. However:

If - since there are specifically 6 cities on the list - Grandpa is visiting one city on each of the 6 civilised/inhabited continents then there is a unique solution...

Since Grandpa has already visited the 3 cities mentioned just now...

This removes all country/city combos in Africa (where Libya is), South America (Peru) and Asia (Bahrain). We now need to identify 3 cities where one each is from Europe, North America and Oceania.

There are only 3 such cities which fill the 4th slot on the list:

[MA]dr[ID] (Spain, Europe) - but no capitals begin with ID so this would end the chain;
[MA]nag[UA] (Nicaragua, North America) - but no capitals begin with UA so this does not work either;
[MA]ju[RO] (Marshall Islands, Oceania) - now we're getting somewhere...!

Following this, Grandpa can only go on to visit:

[RO][ME] in Italy (Europe) and then end his trip in the North American capital of [ME]xico City (in... er... Mexico!). The chain would also naturally end here regardless of the one-per-continent restriction since no capitals begin with TY, so it all fits rather snugly together!

Answer 2

He can go to

MOZAMBIQUE, then CANADA, then JAPAN.

Note the large cities are

TripoLI, LIMA, MAnaMA, MApuTO, TOronTO, and TOkyo.

Note:

It doesn’t say capital cities so Toronto counts, it’s the capital of Ontario at any rate.

As M Oehm correctly notes, he could also go to

The Philippines, Nigeria, and Norway, because of MAniLA, LAgOS, and OSlo.

For only

capital cities, he can go to EQUATORIAL GUINEA, COLOMBIA, and UZBEKISTAN, because of MAlaBO, BOgoTA, and TAshkent.