Pat (oh, Pat.) is sending you to:

SEYCHELLES

Here's how you get there:

First, note that, as Deusovi mentioned, the letters in the invite spell out "VIGNERE" and "REORDER" which tells you that you'll probably need to reorder the flags in some way and then find a key for the Vignere cipher.

Once you figure out that the flags spell out "SAILS", that's the only obvious key. So, how to order the flags?

Because some of the flags are not the flags in current use, it's important to identify when the flags were brought into use. I then thought the solution was to order each group of three by its earliest flag usage. For example, Kenya's group has Spain which began using its flag in 1785, so it's first. Here's where things broke down for me, though. I figured that the smaller flags would be a hint to figure out how to order the larger flags, but couldn't quite figure out how I arrived at my answer. I actually ended up brute-forcing it a bit once I got to this point, as I'd narrowed it down enough for brute-forcing to be a viable option.

KE = Kenya, GN = Guinea, ZW = Zimbabwe, LT = Lithuania, and PK = Pakistan. When you use "SAILS" as your key for that list of letters, you get "SEYCHELLES."

Reverse-engineering it a bit, I think the solution is to take the average age of each group of three flags, and then sorting by oldest to newest, that gives you the correct order.

Pat (oh, Pat.) is sending you to:

SEYCHELLES

Here's how you get there:

First, note that, as Deusovi mentioned, the letters in the invite spell out "VIGNERE" and "REORDER" which tells you that you'll probably need to reorder the flags in some way and then find a key for the Vignere cipher.

Once you figure out that the flags spell out "SAILS", that's the only obvious key. So, how to order the flags?

Because some of the flags are not the flags in current use, it's important to identify when the flags were brought into use. I figured that the smaller flags would be a hint to figure out how to order the larger flags, but couldn't quite figure out how I arrived at my answer. I actually ended up brute-forcing it a bit once I got to this point, as I'd narrowed it down enough for brute-forcing to be a viable option.

KE = Kenya, GN = Guinea, ZW = Zimbabwe, LT = Lithuania, and PK = Pakistan. When you use "SAILS" as your key for that list of letters, you get "SEYCHELLES."

Reverse-engineering it a bit, and with hints, I figured out that each of these groups of two countries have fought in wars against each other. US and Spain was first in 1898, Russia and Japan next in 1904, then Paraguay and Bolivia in 1932, El Salvador and Honduras in 1969, and finally Tanzania and Uganda in 1979.

Pat (oh, Pat.) is sending you to:

SEYCHELLES

Here's how you get there:

First, note that, as Deusovi mentioned, the letters in the invite spell out "VIGNERE" and "REORDER" which tells you that you'll probably need to reorder the flags in some way and then find a key for the Vignere cipher.

Once you figure out that the flags spell out "SAILS", that's the only obvious key. So, how to order the flags?

Because some of the flags are not the flags in current use, it's important to identify when the flags were brought into use. Then, order each group of three by its earliest flag usage. For example, Kenya's group has Spain which began using its flag in 1785, so it's first. Here's where things broke down for me, though. I figured that the smaller flags would be a hint to figure out how to order the larger flags, but can't quite figure out how I arrived at my answer. I actually ended up brute-forcing it a bit once I got to this point, as I'd narrowed it down enough for brute-forcing to be a viable option.

KE = Kenya, GN = Guinea, ZW = Zimbabwe, LT = Lithuania, and PK = Pakistan. When you use "SAILS" as your key for that list of letters, you get "SEYCHELLES."

Pat (oh, Pat.) is sending you to:

SEYCHELLES

Here's how you get there:

First, note that, as Deusovi mentioned, the letters in the invite spell out "VIGNERE" and "REORDER" which tells you that you'll probably need to reorder the flags in some way and then find a key for the Vignere cipher.

Once you figure out that the flags spell out "SAILS", that's the only obvious key. So, how to order the flags?

Because some of the flags are not the flags in current use, it's important to identify when the flags were brought into use. I then thought the solution was to order each group of three by its earliest flag usage. For example, Kenya's group has Spain which began using its flag in 1785, so it's first. Here's where things broke down for me, though. I figured that the smaller flags would be a hint to figure out how to order the larger flags, but couldn't quite figure out how I arrived at my answer. I actually ended up brute-forcing it a bit once I got to this point, as I'd narrowed it down enough for brute-forcing to be a viable option.

KE = Kenya, GN = Guinea, ZW = Zimbabwe, LT = Lithuania, and PK = Pakistan. When you use "SAILS" as your key for that list of letters, you get "SEYCHELLES."

Reverse-engineering it a bit, I think the solution is to take the average age of each group of three flags, and then sorting by oldest to newest, that gives you the correct order.